If you staying with your in-laws, how do define improper attire? Does not wearing a bra considered as improper?

I think it's okay if you know how to conceal the fact that you are not wearing one. As long as the nipples are not showing, it's okay. If you're in the room, wear whatever you want but if you're in public domain, obviously a skimpy top and short shorts will not be a good idea.