I've been following your story, and you desperately need to pursue the single room.
When one is completely overwhelmed with a horrible living situation, it's impossible to fully comprehend what can be obtained through independence through new housing. From my understanding of your story, you have yet to ever live away from your family.
Your pains and troubles are tied into your family situation. You owe it to yourself to break away to experience what life can offer you once you are removed from your brother and father. Be methodical and figure out how to do it properly so you have shelter and don't opt instead for homelessness. Hopefully, the dorm is available to you, but if not keep looking for other suitable options.