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Dear Carolyn: My brother has been married for over 10 years to a woman who I am now afraid is gaslighting him. The situation recently escalated when, after they significantly reduced the dates they could attend a long-planned family vacation, we had to cancel the entire trip since we would no longer meet the minimum-stay requirement. She took this opportunity to lash out at our entire family, saying how our decision to cancel the trip is hurting my brother and their children. She accused us of being horrible people and said she is done talking to us.

Since even before they were married, our brother asked certain family members to alter the way they talk to her and act around her to keep her happy. We have been treading very carefully around her all these years to ensure we can have a relationship with my brother and his children, a difficult road for our once very close and happy family.

They live far away, and we have had to wait for invitations to visit them — my sis-in-law's rules — although up until now, I had more freedom to come than others, as I hadn't done anything she considered offensive.

Her brother and father suffer from mental illness, and I am worried she does, too. My brother and I share an audiobook account and he recently downloaded self-help books, one about how to manage a narcissist.

I'm worried about my brother. He isn't speaking up or giving his opinions at all, just lets her do all the talking. It's very hard to get him on the phone in private, as he works 15-hour days and then is the primary caregiver when he is home. Do I try to call my brother and see if he is okay? My sis-in-law says we need to go to family counseling so we are all nicer to them.

— Sibling

Sibling: Do whatever you must to remain in touch with him. your brother.

Ultimately, it will be up to him to respond to you, but don’t give up easily. Be gently, persistently “there.”

And if there’s a next time: When you suspect abuse and isolation, do whatever you can to leave victims’ lifelines uncut — like book the minimum stay anyway, and just leave when you have to leave.

Even though each of your examples could have a reasonable or healthy explanation — the geographic isolation, the goalpost-moving on the family vacation, the wait-to-be-invited rule, the how-to-train-your-narcissist book, even the sister-in-law’s decision to cut ties with you — all of them in combination say your brother is in big trouble and their kids even bigger.

The most persuasive piece is the one that has no possible healthy explanation, and that’s your brother’s early cue-carding of everyone’s interactions while she was still a girlfriend. If ever there were a one-size-fits-all, “Don’t open that door!!!” horror-movie moment in early dating, that would be it: when one’s new love is so hair-trigger that all must tiptoe to keep the peace.

That is always a false promise, of course. There’s no peace to be had with someone explosive.

But you can’t get a message back in time to his bachelor self, so stick to clear, supportive messages now. Including this: “If you need anything, anytime, call me. No questions asked.” Because it says without saying it, “Emergency.”

Write to Carolyn Hax at tellme@washpost.com. Get her column delivered to your inbox each morning at wapo.st/haxpost.