I am assuming you have legal guardianship of your brother? Can you take him in to get assessed - get his medications and treatment re-evaluated so you have a present-day sense of where he is and someone to ask about his chances for more improvements in behaviour. I find that it's helpful to have accurate information to make good decisions. It also sounds like some respite care would be helpful if you don't already have that, such as people to come in and give you more of a break than you are getting, and who can see how things are and give you someone to share that experience with.
It sounds like your mother had a way of coping with her son's condition that is different from yours, and you get to make choices based on more accurate, present day information than what your mom had. I think that just like it is important to put your own oxygen mask on before assisting a child on a plane with theirs, that it is important to make sure you have what you need to thrive so you can help others to thrive. Some people find that they can be more fully there for an ill loved one if they can find a way to get outside of the daily power struggles by having their loved one live elsewhere. You might find that with some safe space to yourself you will have the breathing room and energy to put in the same love, dedication and care you are putting out now, toward the goal of getting him farther into health that you would be able to now and have the result of making his life (and yours) better than it is now.
British Columbia Schizophrenia Society
A reason to hope. The means to cope.