If it’s your wife’s sister are you able to talk to your wife about this? Then maybe you can decide together what is best for your family and might help you having to worry about this yourself. I suppose at the end of the day though you are not responsible but I get that you want to do your best to protect them. If it was me I would want my sister to know then it’s her choice but I know many would shoot the messenger! I suppose whatever you do if you do decide to talk to your wife/sister in law/friend you don’t actually know for sure so it’s maybe important to say this but also acknowledge that you are worried about behaviours or signs that you have seen. If you have then said what’s needed, you can let them know about support but they would have decide how they deal with this.
