I just need some options and a place to vent, sorry it's long: So a year ago last may my beautiful…

I just need some options and a place to vent, sorry it's long:

So a year ago last may my beautiful twin God daughters came into the world. When me and my husband first held those little bundles of joy we promised them we would always be there for them and that we would always be in their life no matter what. Last fall the mother moved in with the fathers parents and kicked us out of their life when we confronted her about always backing out of plans and such and pushing us away. We were devatsed. I cried for quite a long time. We slowly came back into their lives around and after Christmas but mostly this spring when she finally got her own place with assistance. We did quite a few things this summer together and it was really nice. Then she got a boyfriend and the girls started calling him daddy on their own. He was good with them so I was cool with it. Well then she started having all these back problems and would tell us she couldn't go anywhere because of it. We really don't kno what to believe since a lot of it is common problems and nothing too big. She keeps turning down plans to do anything even go to the nearby park cuz of it. We have had a trip to the pumpkin patch planned for over a month with my other friend and 2 God daughter who r also friends of hers. Everything was fine until I told her I only had room in my car for her and the girls since my husband was coming along and only her and the 2 car seats would fit in the back of my car. She got pissy and said that she won't go with out him and maybe she can borrow her mom's car. It made me feel really upset that she would back out on that just cuz of that. she said that he is their daddy and shouldn't miss their first trip to the pumpkin patch. But this guy has only been in their lives for like 4 months....i feel like he comes before us who has been in their life since day one. To be fair we havn't seen them much due to working so much but she hadn't messages us either asking about coming ovr or telling us how they are and then get mad and say that we make no effort. Idk what to do I want to keep my promise to these little girls who I love so much but she is making it so hard especially when she can't do anything or go anywhere with out him. Thoughts?