Dear Carolyn: I just found out that my niece's husband has made inappropriate comments/propositions to both of my daughters, one still a minor (17). I have to tell my niece, right? I can't see a way out of telling her, but it breaks my heart. I don't want to hurt her.
— Broken Heart
Broken Heart: You're not hurting her, her husband is.
As for whether you "have to tell," that depends on the comments themselves. I realize we're in the midst of a massive and long-overdue awakening to the fact that male sexual aggression toward women is an abuse of entrenched power, and so discretion is arguably the more radical advice than disclosure. However, "inappropriate" is still a big category and still defined by the beholder, and there's still a lot of room between "You look hot in that dress" and grabbing your wife's teenage cousin by the pantry.
So I suggest using this standard for unwelcome, awkward, possibly family-disrupting judgment calls: Telling others only what you yourself would want to know in their position. And would you really want your aunt notifying you that your husband just told so-and-so she looks hot in that dress?
Your younger is 17, not 9 — and you don't stir a family pot unless you have darn good cause.
I realize this risks letting your nephew-in-law get away with skeevy behavior, but he and your niece are adults and as such get a fair amount of leeway to make bad, gross or ill-informed choices. A threat of physical or emotional harm — if your daughter really were 9, say — means you speak up. If everyone just thinks your niece married badly? Stay out of it.
Re: Hitting on My Girls: He has professed "feelings" many times for my older daughter, and it made her so sick. She is very close to my niece. We told him to never talk about that again. He stopped for about a year but started up again. And now I've found out that he twice asked my younger one to play strip poker with him. My girls didn't know how to handle it other than to tell him to stop. Should I tell my niece? She might leave him for something like this.
— Broken Heart again
Broken Heart again: Perhaps she should.
It's a pattern; your daughters said no and he's still pursuing them; and your niece is apparently oblivious. If presented with those facts myself, I'd tell my niece. No — I'd monitor closely, but urge my daughters to tell their cousin themselves, even the 17-year-old. She is, presumably, out on her own more than she's with you and therefore needs big-bad-world advocacy skills. They tell him no, they walk away, they tell their cousin. Empower them to empower each other.
To: Broken Heart: Take care to support your daughters. Tell them the husband is crossing a line, e.g., "It's not your fault. It's a power play by people who think they can get away with it. Do not be shamed, bullied, gaslighted or intimidated into tolerating it, not even for fear of upsetting your cousin. Do not make excuses for it. Do not stay for more. Say, Stop. Knock it off. Slap handsy hands. Don't fear making a scene."
Anonymous: Amen, thanks.