Been with my DP for just over two years, we have a 4 month old DD. He has two DD from previous relationship aged 5&6. His ex has also had another baby with her partner.
They don't get on very well and communicate through either me or her Nan. We tend to get on ok until she decides she wants to hate me every so often. When this happens I get randomly blocked, phone gets ignored, kids tell us she hasn't been saying nice things about me, it's all a bit dramatic tbf.
So skip to two weeks ago, we are going on holiday abroad soon, DP always pays for the holiday so I always pay for the new clothes for us and spending money. Girls come shopping with me and my DD, pick new holidays clothes, trainers etc..
They get dropped to their nans later, then i get a message saying "I'm sick of you always trying to embarrass me by buying the girls clothes and shoes all the time! They're not coming on holiday with you, and DP will have to stay at home with them" (She has always booked a holiday with her partner and son and her partners daughter whilst we are away) (Also, our holiday is with DP's dads family). I told her she's being ridiculous and to message me when she's back in a normal state, to them be told she's reporting me to social services for taking cocaine when I was pregnant and "No wonder your daughter has problems"! Shes a known story teller (been pregnant with my DP since I've been with him, her DP is buying her a Range Rover, she's putting the girls in private school) none of this has ever happened, so of course this hasn't gone anywhere,
Anyway, every time she has these hate vendettas towards me she doesn't let DP see the girls. We usually pick them up every day from school, feed them and they stay over on the weekends. When she likes me they stay in the week 2 nights too. Me and DP have been having major domestics as he blames me for antagonising her by buying the girls new things 
It's making him really upset as he misses his girls and the only way she'll let him see them again is if we split up.
We love each other very much and I would hate to leave him as my DD needs her daddy too!
What do I do ? 