Can you help me solve drama with an ex?

Here it goes i'm having Major issues with my husband and his ex-wife. First she ALWAYS take advantage of him and me. he has two children with her. I love these kids like their my own do everything in my power to help them with whatever they may need. The mother works I work and so does my husband my hours are very different from theirs I work 4-5 hours a day 7 days a week. Then take care of 4 kids and a home and a husband. T he major issues im having is the ex is always taking advantage of my husband and me. the kids are here every day i cook for them i clean up after them i do it all. I never get a thank you nothing. the other day for their fall break she doesn't even ask if the kids can stay she just doest bother getting them until 5 days later. My husband never said a word to her.then wouldn't you no it this week one of the kids got sick she telling my husband take him to doctor(he did need to go) get him this and that.(medicine) when in the agreement its her responsibility to pay co-pays for the docs. She wont pay the co-pay we were out taking him to the doc.That don't bother me he needed to go. the thing is she makes dam sure when theirs something we have to pay she on it big time. He ALWAYS pays his child Support never late. Now me and my husband are having Major trouble only because he can't tell her NO about anything. Its driving me up a wall.