My MIL in the over 20 years I have known her has always made up bizarre stories and motives for other people behavior. She is very paranoid and isn't able to ask people why they behave in the way they do instead she creates her own narrative. In the last year she admitted in letters to DH she is having delusions, very serious ones in which she believes different men are "coming out of their bodies" and coming to her at night and having sex with her.
Despite family denial I am very glad to say that DH and SIL were able to persuade her to start seeing a very experienced counselor - which DH and I are paying for. This has not started yet.
In the meantime DH has planned a holiday for us all including MIL. Although I am willing to go I feel very conflicted and uncomfortable as my DH and SIL seem to be sinking back into a state of denial about MIL. When they are all together they behave in a very emeshed way almost as if they are on an emotional high and are 1 being rather than 3 people. It is very weird to witness. I will be going but how should I behave in this scenario? MIL and DIL are both divorced so I will be the only unrelated family member.