I had a rather different situation but none the less awful....
Daughter got rather close to another man but nothing happened just lots of texting, told me far too much about it, worried me to death and the next day I had SIL at the house in tears and desperate, asking my advice on what to do. I was stuck in the middle!! SIL was not sure, he just had an idea daughter was infatuated with someone else. I'm afraid to say I just played ignorant, pretended I knew nothing and told him not to worry etc. He was imagining things. Didn't know what else to do. Daughter got a right bo**ocking after from me. Told her to make a decision and not hurt SIL. It's blown over now, phew ! Nothing came of it, but have told daughter not to tell me anything else, but then again I want her to know she can discuss problems with me. It's such a horrible situation to be in and I was not prepared for it.
Mental health worry in grandchild