Yes,  a really messy home can contribute to ones mental health.   If the house was on fire the first time that means house is not safe.   

But the idea of living as a disabled. religious brother is a great idea.  

Many of us have things in our homes that we don’t need.  Think about how our ancestors lived.  Houses without electricity and heating. They didn’t shop for Knick knacks because they had zero money.  We are guilty of this. I have been guilty of it. 

They are your parents. It is hard.  Talk to them. Show them videos from YouTube  on how to clean up for motivation.  Save money up and get a hotel room for a couple of days for your parents. Or have them stay with your brother or other relative. Then while they are away, clean the house up as a surprise.  

I dont believe its a good idea to send parents to an hotel room and cleaning as a surprise.
They like their mess. 
They are not disabled or too tired after work. I know ehat Im talking about because my mom lives in a messy house.

One day, I tried to clean her room and she was very polite and appreciated it but she was also confused and I knew she didn't like it.

She had a difficult time finding her things even when I put everything in a logical order (!!!). In her own messy "system" she found everything she needed.

Maybe you can clean up the common spaces but I believe its not a good idea if you dont talk with them BEFORE.

I believe the messy house its your Cross. Not the messy house but living there and having to shut up. Maybe you are the kind of person who wants to control everything (Im one of these) and this is a way to understand that you cannot control everything and have to shut up and remain humble.....

But you are a disabled person and you have your mental issues, so I dont know if this is going to be good in a spiritual sense.... you have two choices, I told you.

I just wanted to let you know I was still thinking of your situation, and hoping you find peace in it. 

I replied in very hard terms to the OP so I apologize to him.

I am the OP. The hard terms were good for me so I thank you. What I get from this thread is that I was overstepping my authority as a son and that I should just keep my two little corners of the house clean and try to be a good example and leave my parents to their mess. About not giving my brother money. I promised that I would help him so I feel obliged to help him for this one last semester so that I would keep my word.

Hello.  I have several family members who choose to live a cluttered life and I've also watched many many hours of "Hoarders".  Hoarders are very spiritual sick people who struggle with severe pride and complete resistance to getting rid of their hoard.  The hoard is a proxy for the loving presence of God in their life.  The hoard gives them comfort, protection, and keeps them from feeling lonely.  Until the hoarder can fill up their life with those things they will NEVER willingly give up the hoard.  They also use the hoard to manipulate and control others who hate the hoard.  Hoarding is usually triggered by a severe loss in the life of the hoarder, such as death of a loved one or other traumatic event.  Some have started hoarding because of divorce, adultery, drug/alcohol use of a family member, or loss of income/status in the community.  The hoard is a warped attempt to self soothe.

OP...your parents are classic hoarders.  Hoarding is a mental illness and simply cleaning up will not cure their problem.  You are correct that the origin is spiritual.  I'm not in a position to list out saints/moralists who teach that we should limit our contact with those who are detrimental to our own spiritual life.  It's so very hard when it's your own parents, but please know this....I've spoken to half a dozen solid traditional non-compromising priests on my situation with a parent.  The message was the same:  we are obligated to assist IF they need financial/physical support.  However, we are NOT obligated to have a relationship with a parent who is antagonistic towards our faith.  You can assist them from a distance by paying a bill for them directly to the creditor.  Such as an electric bill or rent.  Drive them to appointments.  Since they are not good stewards of your generousity you should not give funds to them to spend as they see fit.  I have suffered for many years over having a parent who lives in squalor and hated towards my Catholic faith.  But I have confidence that God knows my heart and that I crave a relationship but this parent won't allow it.  Good luck and God bless you.

If you need help making some decisions I can put you in touch with someone who does coaching.  

My parents respect my faith, though they disagree with me. They have always allowed me to go to the Latin Mass and before I had disability they would give me money to go to Mass and give to the collection and often drive me. So they are supportive and not antagonistic. So they are not a danger to my faith. I like living with family more than I would living with roommates who I do not know. Which is why I stay. I just know that it could be better and wish it were already so.

I don't think I need a coach per se but I am grateful for the offer. I have some questions here and there and usually asking people online and thinking about their advice helps. And if not a I can always ask our priest or a friend or my therapist or doctor.

I believe it doesn't apply the "against the Faith card". Your parents don't have the faith but they don't opose you have it.
You can move on anytime you want, you are a free person: you are not married to them, you are and adult. Dissability don't make you an under age minor.
If you leave, you cannot abandon them, so you have to take care of them specially as they are getting older. You can move out but you can't forget them.
But, if you preffer to live there, it's OK. You have to obey your father's rules and don't try to change things against his will (or your mother's).
You have to live by their rules EVEN if they are messy people.
If they respect your catholic view and practice of the Faith, it's OK.
PS. Your brother is another thing.