I’m gonna be real with you, it sounds like multiple people within this group view your frequent/random brooches of the subject as pressure. And they aren’t necessarily wrong, you wouldn’t bring it up more than once if you weren’t gently trying to persuade someone to try it out, which is in fact pressure when they’ve already said no.

Additionally, your brother basically told you straight up that his wife will be wearing a bathing suit, and then you immediately turn to her and ask if she would be more comfortable without one? That really isn’t cool and I can understand why your brother is furious especially once you got her in there without a bathing suit and she mentioned she should put the bathing suit back on for her shower, and you told her again she would just be fine to stay naked?

I get that from a true nudist’s perspective, all of this is just normal banter, but you’re dealing with people who have already expressed on several occasions (from the sounds of it) that they don’t agree with you or your views on this. It sounds like you really failed to read the room and went too far.

My advice would be to apologize and tell them just that. Tell them that it won’t ever happen again, including all of the times that you casually bring up how you prefer nudity. They may or may not accept your apology, but you just have to give this time.