It's an interesting question, MaggieTulliver and started me thinking about how this seemed to be more the norm than it is now, perhaps because sisters were left unmarried if their fiances had died in WW1, sisters looked after bachelor or widowed brothers.
My widowed aunt had her bachelor brother to live with her, it seemed to work quite well, and two other aunts, both widows, lived together.
More recently, our neighbours were siblings too, living with their mother, but all deceased now.
It depends how much you both want companionship and whether or not there is room for you both to have your own space if you so wish from time to time.
Alternatively, could he stay on in your mother's house and pay rent to the co-owners if they are agreeable.
I don't know anyone now who lives with a sibling though.