My daughter is divorced. She and her exhusband spend every Christmas day together with their young children taking turns to make Christmas dinner and they share childcare equally.
So they aren't all selfish.
However I do sympathise. Your grandchildren aren't getting the care they should. Its important that children feel secure and loved even though parents are separating. Its good that they have caring GPs. I think you should offer to see them as much as you can manage, as being with you will provide some much needed stability.
CUTTING OFF A ROSE BRANCH IN NEXT DOOR'S GARDEN