This is a complex one. NC as very outing. I really don't know how best to handle it.
My DD's father / paternal grandparents were very emotionally abusive to me but have never (previously) showed any signs with her. We split whilst I was still pregnant, I've worked very hard to build a good, stable family dynamic and co-parenting relationship. Standard alternate weekends arrangement, she lives with me through the week. On her Dads' weekends he chooses to let her stay with the grandparents quite often because he works a lot - for same reason, they tend to have her for most of his share of holidays. She is now upper primary school.
She used to have an excellent relationship with the grandparents, but in the last year has started getting very stressed about going there, nightmares when she comes home etc. She recently opened up to me that the grandmother in particular is very emotionally abusive - makes her spend hours doing things she wants to do but refuses to talk to her about or do anything she likes. Gets explosive over things not going exactly the way she'd planned. Tries to "teach" DD lots of high level things (she used to be a teacher) but then gets angry if she can't grasp them. Calls her bigoted if she has a different opinion to her. These are just a few of many examples. I believe DD as this is exactly how she used to be with me. The grandfather on the other hand does a lot of blackmail if she doesn't want to go "we won't be around forever" etc.
I spoke to exP and said this really has to stop, DD is dreading going to theirs and doesn't want to stay for long periods like holidays anymore although she doesn't mind seeing them with him. I thought, naively, that he'd back her corner but instead he's got cross and said if that's how she feels, she needs to tell them this herself at a formal meal he's organising. And that she should expect they'll give away all her things etc. He also keeps pressuring her to make a decision re: all holidays and weekends for the rest of the year because they book so far in advance.
I just don't know how to help. DD is adamant she doesn't want to cut contact altogether or ruin the relationship. But she's also v stressed and unhappy and I feel both her grandparents and dad are treating her abusively. If I weigh in, it's likely to turn very nasty as they are all the kind of people that if you disagree with them they dig their heels in more and twist the situation. And whilst I absolutely don't mind fighting DD's corner, I'm concerned I may make things worse for her.
Sorry that was so long - any suggestions appreciated.