A picture is worth a 1000 words. There is no other way to show what they look like except to take the actual pictures at the chapel.

That's your opinion.  It would be different if you posted ACTUAL pictures of what took place at the chapel.

But, again, if the immodesty is sinful, you are sinning by posting these pictures.  Your need to VENT about that chapel is not sufficient justification for it.

Top one is fine. Ideally it would be better, but I wouldn't consider a girl immodest if that's how she dressed. Second is immodest. The third - the t-shirt is immodest, the skirt would actually be fine if it wasn't so tight on her(and I agree, she looks stupid more than anything, she needs clothes that actually fit first of all).

Now, I disagree that the first one is OK.  Skirt length is clearly above the knee, which according to the Church's standards, is in fact objectively immodest.

Now, what LOT of people forget is that immodesty, like any other sins, does admit of degrees of gravity and/or veniality.  So, for instance, having an otherwise-modest sleeveless shirt is simply not the same thing as walking into church wearing a bikini.  Some people seem to think that it is, that everything related to modesty is grave.

So, for instance, the first picture would be venially immodest, while the second begins to approach gravely immodest.  But I don't think you could excuse either of these from immodesty to one degree or another.

A few months ago I was chatting with the priest after Mass. He looked over at a young woman and then asked me to point out her mother to him. I did and he immediately went over to the mother and discussed the length of the skirt the daughter  was wearing. I walked away but did hear him tell the mother that her daughter was not to wear that skirt anymore.

Indeed, the priests are in a difficult position.  Ideally, the priest should designate some older women of good reputation to be the modesty enforcers.  If you're a priest and walk up to the mother to make that kind of comment, this could easily be turned into:  "Why, are you checking out my daughter?"  Then the disgruntled mother would start wagging tongues about the priest, destroying his reputation, for checking out her daughter.  So the priest should delegate this duty to older women who could be trusted to carry out these duties appropriately.  He, then, of course, being guardian of the Sacraments, could/should withhold them from those who are in serious violation of standards, but apart from that he should leave it to the old ladies.

I say this because I witnessed this dynamic take place against one particular priest, so the young priests and seminarians need to be instructed at seminary regarding how to go about this.

This is not about an occasion of sin for me, it is about the bad example it sets for all of the other younger girls in the chapel, it is a mortal sin for those girls who wear those clothes and scandalize the little ones:
 “It were better for him, that a millstone were hanged about his neck, and he cast into the sea, than that he should scandalize one of these little ones” (Luke 17:2)

Well, I don't disagree, in general.  #1, IMO, would be closer to venial in general, but it's certainly compounded by the fact that it was at Mass.

Is this a systematic problem with the SSPX?  Another sign that the SSPX is becoming more modernist?

This could have been handled with a, "At the Sanford SSPX chapel, no attempt is being made to enforce standards of modesty."  I just don't think that the excessive huffing and puffing accomplishes anything.  Nor does posting pictures of samples.  Even if you were to post actual pictures, it's one thing that it's happening and QUITE ANOTHER if the priests are condoning it.

Perhaps it's a misguided prudential judgment about not wanting to harden their hearts and drive them away.  Maybe it's cowardice.  Perhaps it's that the priests aren't fully aware of the extent of it.

Have you even tried to go to the priest and said, "Father, there are women and young ladies here whose skirts are well above the knee.  Can't you do anything about it?"  I would be more interested in Father's response than in the mere fact that women are showing up there in short skirts.  His response could speak volumes about the state of the SSPX.  Would he say, "you're a bit of a prude" (ala the Theology of the Body crowd) or else "You're right, I need to try harder to enforce the standards." or "You're right, but I don't want to drive them away."  I know one priest who simply responded with, "Well, that's just what the young people are all doing these days."  (Yes, this was a Traditional priest).  This seemed to come from a combination of laziness and a fear of confrontation.  So I'd be more interested in the Father's response.

THEN, if the response is not acceptable, I would put the US District Superior on the spot, "Father N. said ....  Is this the official position of the Society?"  That I would be even MORE interested int.

Why don't you track it down this way rather than just venting anonymously here on CI?

Then I'd tell Father, "Father, if some young man came up and told you that he couldn't go to Communion because he was tempted to a sinful thought during Mass by one of these, what would you say or what would you do?" Would he say, "well, that young man needs to become more pure and toughen up"?  To which, I would respond, "Well, that's not the Church's teaching on this subject, that this is merely a scandal of the weak.  Shouldn't a young man who assists at Mass have the right not to be distracted, much less tempted, by immodest dress?"

A few months ago I was chatting with the priest after Mass. He looked over at a young woman and then asked me to point out her mother to him. I did and he immediately went over to the mother and discussed the length of the skirt the daughter  was wearing. I walked away but did hear him tell the mother that her daughter was not to wear that skirt anymore.

If this is the same priest, then he's doing SOMEthing.  But what's the next step if the girl shows up again dressed like that?  I could see the girl wearing a similarly immodest dress, but not the same one, and respond, well you didn't tell me not to wear THIS dress.

I knew a priest who regularly preached against immodest dress.  For a week or two, things would get better, but then after a little while it would slide again.  First you had one woman test the waters with a slightly short skirt.  When she got away with it, then a few others came the following week.  And within about a month they were back to veritable mini-skirts.  Then the priest would preach about it again.  And this cycle continued for years.  At some point there needs to be SOME kind of actual enforcement.

On an amusing note, I guess, the primary woman who was always the trailblazer in pushing the limits, the one who tested the waters, got poison ivy all up and down her legs shortly after one of these displays of testing the water and had to wear an ankle-length dress for a few weeks to hide the disfigurement caused by the ivy.

Well, I don't disagree, in general.  #1, IMO, would be closer to venial in general, but it's certainly compounded by the fact that it was at Mass.

Is this a systematic problem with the SSPX?  Another sign that the SSPX is becoming more modernist?

This could have been handled with a, "At the Sanford SSPX chapel, no attempt is being made to enforce standards of modesty."  I just don't think that the excessive huffing and puffing accomplishes anything.  Nor does posting pictures of samples.  Even if you were to post actual pictures, it's one thing that it's happening and QUITE ANOTHER if the priests are condoning it.

Perhaps it's a misguided prudential judgment about not wanting to harden their hearts and drive them away.  Maybe it's cowardice.  Perhaps it's that the priests aren't fully aware of the extent of it.

Have you even tried to go to the priest and said, "Father, there are women and young ladies here whose skirts are well above the knee.  Can't you do anything about it?"  I would be more interested in Father's response than in the mere fact that women are showing up there in short skirts.  His response could speak volumes about the state of the SSPX.  Would he say, "you're a bit of a prude" (ala the Theology of the Body crowd) or else "You're right, I need to try harder to enforce the standards." or "You're right, but I don't want to drive them away."  I know one priest who simply responded with, "Well, that's just what the young people are all doing these days."  (Yes, this was a Traditional priest).  This seemed to come from a combination of laziness and a fear of confrontation.  So I'd be more interested in the Father's response.

THEN, if the response is not acceptable, I would put the US District Superior on the spot, "Father N. said ....  Is this the official position of the Society?"  That I would be even MORE interested int.

Why don't you track it down this way rather than just venting anonymously here on CI?

Then I'd tell Father, "Father, if some young man came up and told you that he couldn't go to Communion because he was tempted to a sinful thought during Mass by one of these, what would you say or what would you do?" Would he say, "well, that young man needs to become more pure and toughen up"?  To which, I would respond, "Well, that's not the Church's teaching on this subject, that this is merely a scandal of the weak.  Shouldn't a young man who assists at Mass have the right not to be distracted, much less tempted, by immodest dress?"

Thank you for your opinion, but you do not comprehend the motive or the extend of the problem. The extent - I am not writing here to "vent" about my chapel. I am writing here to expose a problem that has not be addressed at all by the SSPX in the USA and Europe, the two places that I have knowledge of. It is a problem that rose up like 10 years ago and now is common all over the USA and Europe. My area of direct exposer is the USA and specifically the St. Mary's Kansas Church and town where I believe they have 5000 parishioners. The same goes for the school in Syracuse, New York. Sanford Florida also has a school but it is insignificant. What all three have in common is that not a word is being said about the way the young girls and Latina women dress. The Motive, I am here to expose this situation to the SSPX priests worldwide, including Bishop Fellay. This is not about talking to a priest is Sanford. 
Those young girls just need to be taught how to live the Catholic faith or else there will be no future generations of traditionalist for the SSPX. The clothes they wear to mass is just the tip of the iceberg, the most "modest" clothes they wear all week! The rest of the week they wear the same clothes and do the same things as any worldly girls. The only difference is that they go to mass on Sundays. THAT is exactly what happened in the 1960's, I've been there and done that.