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

My MIL walks out of her room wrapped in a towel, more than half of her fat and old body is exposed, my BIL comes home and starts stripping until he is left with a underwear and walks ard like he is alone. Me not wearing a bra underneath my clothes is not going to be a major issue.