Fortunately or unfortunately, they'd let me stay.
Besides, as I've mentioned, he does pay for some rent, he's away ten times a year and works long hours. How much of a burden is he on the family home, in all honesty?
Even then, this is a conversation for the parents and the brother. Not OP, IMO.
If my sister was doing this I'd really have no say in the matter, and vice versa.
He pays "some" rent. Who pays the heating, electricity, food, cleaning products? Does he cook? Clean? DIY?
My parents would not think twice about having me back in their house with my wife and kid in tow, if God forbid, something happened and it came to that. However, they'd expect me out as soon as it was feasible/comfortable for us to stand on our own feet again. I'd hate to think I was taking advantage of them in their twilight years.
I do not understand this molly-coddling attitude towards fully grown adults. The man is 40 for Christ's sake. 40! It's pathetic.
As for asking your parents what they want to do, it's quite possible that they don't want him there, but are too fearful to say anything. We had a similar situation in my wife's family, except it was her grandmother living in her uncle's house. They were ripping her off something rotten, we offered to step in, but she said no "I don't want a fuss". She lived with it, and complained bitterly to us in private until the day she died. Afterwards, we wish we'd done something sooner or got her out of that house. So yeah, older people often lose confidence and bottle it. They might not say something for fear of "creating a fuss" but in fact could be miserable with his selfish backside hanging around like a bad smell.