There is no such thing as same sex marriage, so how is it possible to attend something that doesn't exist? 

If your niece or nephew started murdering people, would you get together afterwards to celebrate their new life of crime to keep peace in the family?

You cannot serve both God and mammon. Sodomy and lesbianism is a sin that cries to Heaven for vengeance, should we go just to make sure auntie Margaret doesn’t think we’re too backwards and hateful? Then Our Lord will not say “Well done, good and faithful servant,” but instead “begins from me” because we loved creatures more then Him. 

You're seriously asking this?

poche, that you?

No!  Why would you even want to attend?  This isn't a matter of showing basic respect, ie. attending a non-Catholic funeral for family or professional reasons.  It's a matter of celebrating mortal sin.  You probably can't do or say anything to stop the people; they're going to do what they want.  My best advice to those who know that voicing or otherwise making the truth known will make matters worse, drive the people further into sin, is to ignore the so-called marriage and avoid those involved as much as possible.  Treat them as you would strangers.  If you must interact with them, be cordial, be polite, be brief, and be gone!  
If this means cutting family ties, so be it.  Replace them with friends of sound moral character.  If you can't find any, keep to yourself and give more time to God. 

No. It is not “ok” to attend same sex wedding.  If you go, you are condoning mortal sin.  And no attending weddings of divorced and remarried either.  

I say no.  Even most Novus Ordo websites confirm my no.

If one of you had a cousin or niece who was getting married to a member of the same sex would you attend the reception, just to keep the peace in the family?

If they even were to invite you, then take that as a wake up call that you are doing something wrong. You should have disowned them - and they should know without any doubt whatsoever that you've disowned them, probably a long time ago. No way should they even think about inviting you.

If you want to keep peace in the family, then break all ties and do not associate with them in any way. Pray for them certainly, keep praying for them, but stay away and keep the rest of your family away from them at all costs. They are too far gone for any "dialogue" whatsoever at this point and can only bring disaster to peace in your family.  

If they even were to invite you, then take that as a wake up call that you are doing something wrong. You should have disowned them - and they should know without any doubt whatsoever that you've disowned them, probably a long time ago. No way should they even think about inviting you.

If you want to keep peace in the family, then break all ties and do not associate with them in any way. Pray for them certainly, keep praying for them, but stay away and keep the rest of your family away from them at all costs. They are too far gone for any "dialogue" whatsoever at this point and can only bring disaster to peace in your family.  

This is spot on! It was in my mind to say exactly that but I don't put it down so well.

When my only sister's two daughters married outside the church within a couple of months of each other I was not even informed They were getting married.

They know where I stand even though we have never discussed it. I am forever on the outer. I like it that way.