My brother wants to file his taxes, but what if he passes before check arrives? Anyway he can sign it over to me, his sister?

If brother is on Medicaid he can’t just sign check over to sister. That is gifting. If he lasts longer than you think he may, can you take over if Medicaid is busted? Be careful.

Ask your brother to have it direct-deposited to an account that you have access to. The money gets received by him faster and it's more secure. And you can access the funds for his needs or for whatever he decides (or it becomes part of his estate).

It becomes part & parcel of his estate, anyway how can he sign it over to you if he is dead?