I've insulted my in-laws, what to do?

I understand that you want to keep your daughter safe and that you are upset that they basically ignored your concerns for your daughter safety (I would be too). But I can also kind of see why they would be upset too (I would be upset if someone practically accused a family member of mine of being a potential offender). However you did mention you brother-in-law was strange and unpredictable so I can understand your concern, even though I would have a better understanding if you tell us what makes him so unpredictable. I would talk to your in-laws and your husband and explain to them how you don't want your daughter to be left alone with a man you don't know well or feel uncomfortable about. If they can't understand that then I would keep your daughter close to you as much as possible.