Your family have been through alot.
You may be struggling with some kind of secondary trauma yourself, as you speak about them with clear love and understanding.
I had 2 DSC myself when I was very very young (exH and I had almost 20 years age gap) and both my DSC had NC with their mother who had been abusive and negligent towards them.
Their behaviour was a lot to take on some times, because even though I understood why they behaved the way they did, I didn't understand how to combat it.
That was a long time ago now, since then we understand trauma, abandonment etc far more.
I'd suggest reading books, both you and DH by Sarah Naish, A-Z of therapeutic parenting when you can, also a book called The Primal Wound by Nancy Vetiver to start off, treat their parenting style how you would kids you'd adopted from trauma, even if they're with their dad, there is obviously alot of damage created by time spent with their mum.
I wish with hindsight I'd have known more about therapeutic parenting as opposed to getting into unnecessary power struggles etc with my SKs, I also felt wholly unappreciated, no matter what effort I put in, but now I know more about parenting I wonder if I struggled with that because I'd have liked a parent like me, which was my issue, not theirs.
I think therapy for you all to some degree needs to happen, you sound fed up, but not like you want to leave.
It'll be a tough slog for you and DP, but it really could be worth putting into it, so you don't have to lose your DD 50% of the time.
I have lots of book recommendations and YouTube suggestions on therapeutic parenting if you'd like them, I have read loads on the matter as we'd have quite liked to adopted, but it wasn't to be in the end for us.
I understand that negativity is totally draining, but it can be combated with lots of logic and positivity, (eg a kid moaning about the rain, "think of the plants that need watering") very weak example but its very early 😂
Good luck with whatever you decide to do x