L.M.
I am totally with you. My husband's mother is not nearly as much of a culprit as his grandmother. She is always saying I should call on her to come visit when I need "help." My husband is deployed and i have three kids. My three year old son is big for his age and i have six month old twin girls. The grandmother in question is always saying she'll come for a visit when she gets one ailment or another behind her. (Anything from planters warts from kidney stones.) yet with all her issues, she expects to be able to watch all my kids while I run errands or have a doctor's appointment. Not happening. My husband also has issues with his grandmother's preferential treatment towards the girls in his family.
i could go on about the issues I have with members of hubby's family, but it doesn't matter. I don't tell them they can't visit, and i occasionally go out of my way to provide opportunities for a quick visit in other venues, but I don't understand this obsession with spending time with my kids without me around. The more people push for it, the less likely I am to accommodate.
Also, I am sick to death of the argument, 'So-in-so raised your husband and they turned out Ok." Fallacious logic! My husband grew into a decent man in spite of the influences in his young life, by his own admission. Also, there are far more factors in the upbringing of a child neither blame nor credit can be laid at any one person's feet.
So.... my advice would be to not put your husband in the middle any longer. His mother is not going to change. You and he need to come to some sort of agreement regarding how much exposure you will allow and under what circumstances, and be prepared to implement that. You don't have to be mean or vicious, but you don't have to bend to everyone else's wishes. these are, after all, your children.
best wishes to you.