We're all going away for a family holiday to celebrate my mum's birthday later this year. My brother divorced around 2 years ago, and I can't get away with his ex. She's obsessively clingy with their DD, to the point she doesn't let DD stay with him unless she's present. Therefore, they go on holiday together still, brother has very little time with his daughter without her being there, despite him being a wonderful father. He has a son from a previous relationship who is 18 and he's got an amazing relationship with him. His ex is extremely manipulative, looks down her nose at us all, is generally nasty about us all. We're generally just happy to have a civil, passive relationship with her as we wouldn't want to be mean to her face. He's just text to say that she wants to come on the holiday, otherwise she won't let their DD (5) come! He's very defensive of her. Under normal circumstances we will tolerate her and be pleasant, but WIBU to tell her actually this will spoil my mums birthday if she comes and to not invite her?