What you're talking about sounds familiar to me. Except the sister. It sounds awful living with her.
Do you think you might get some more private space? If I were you I would try not to run into her so often. Maybe the whole situation gets a littler more relaxed then.

I also experienced that it can be very hard to get anybody to see that you need help and then actually get it. It took me several months to only get an appointment and then it was a complete disaster because the person I saw only wanted to get rid of me as quickly as possible and said some things that were really upsetting.

That whole thing about being important for society is tricky. Of course you should think that of yourself but sometimes other people don't and you need to be strong enough to ignore them.
While looking for a job I have explicitly been told that my education was useless and I do not qualify for anything or any job because all I learned isn't important in real life and I just had to accept that society doesn't need me.

People can be very ignorant because they're busy with their own problems and just don't think about what their behavior may mean to somebody else.

I am just a few years older and have realized that they often can't imagine that someone who is young and appears to be on a good way in life could have any problems. Sometimes it's hard to tell what's really going on because everything looks just fine from outside and even when you say that you're not fine nobody can understand it because they cannot see it.