Your brother-in-law is too business-minded. Here's a suggestion for you. If you do it with your brother-in-law now, you won't get much benefit. If you don't go, I guess your brother-in-law is still doing his upholstery store. His brother may not be able to go with your brother-in-law either.

So, I suggest that you don't go for it for now, and then look for other car-related stores in your city, and then work with them in the way that your brother-in-law said, and see if there are any that you can work with. If not, then make your next move. Stall your brother-in-law first. See what he does. Don't act like you can't do it without him.