I think that what you are doing is very commendable. I think you are doing what you think is best for him right now. My concern is why you are questioning what you are doing? Is there something that is making you doubt yourself? I know it must be very hard for you to take in another person, brother or not.
I think if you and your brother get along and there is no reason not to trust him or have him there, then you are doing the right thing.
Just remember that at some point you may not want him there for one reason or another. I did that with someone and I loved them dearly, but after a while, I just needed my space back!
Anyways, I think you are a very kind person and I hope this helps a little.