My 29F sister 34F, let’s call her P, used to have a podcast where one episode she had our eldest sister 37F, let’s call her F, and our brother-in-law, let’s call him A on it. F and A have been together for 18 years, married for 7.
Recently, P received a message request on Instagram from a girl, let’s call her Q, asking “are the couple from [episode #] still together?” P said that Q initially messaged in February, then again in March and again in April. Q sent a message 4 days later saying that she is seeing A and that female intuition led her to further investigate as she didn’t fully trust A’s words. A has told Q that he and F are no longer together because he says that he and F went into an open relationship but when F started seeing someone else, A couldn’t take it and thus ended the relationship.
I know for a fact my sister would never enter into an open relationship. She is Catholic through and through and shares a child with A. Their child is their rainbow baby, and she prayed day and night for a successful pregnancy which finally came true in 2025. Nowadays, in between work and taking care of the baby, my sister would not have time to have an open relationship.
For context, my sister and brother-in-law do not live and work in the same country. He moved to his respective country in 2023/24, but he visits from time to time and she flies out to see him too. When my sister was nearing the end of her third trimester, she and her husband stayed in the country where she wanted to give birth. Everything seemed/seems dandy. We recently celebrated their child’s first birthday and nothing seemed awry.
My sister and I are both stumped. P has replied to Q asking for more information to fully understand the situation and in order to share some more information back. No reply yet.
How do we go about the situation? How do we tell our sister when we don’t have proof and it might cause trouble? Do we confront our brother-in-law without our sister knowing? P is closer to A, she helped him plan the proposal to F many years ago so she’s thinking of confronting him herself.
TLDR: Sister received a random messaged from a girl claiming to be seeing our brother-in-law. We’re not sure what to do.