M.
I can so relate to this. My step son stays at his grandma's every time we have him, and he knows when he goes over there. he won't eat at our house and then goes there and just eats whatever he wants, and she doesn't care. he won't his his dinner there, but then he gets to eat ice cream, pudding, jello, candy, cheetos, chips, whatever he tells his grandma he wants. plus he gets to do whatever he wants. there are no rules at all over there, and that i don't like. I told my husband that his son should stop being over there so much, and soon he will, when school starts, but my husband's response is, well, it's always been that way, so i don't want to change. Even when she comes over, his son, doens't think he needs to listen to anyone. And then grandma stands up for him. When he got in trouble, she said " oh he was showing me the toys" and he was told not to play with the toys at least 3 times that day. they weren't his to play with.
Grandma even told me that she will do the same things with my daughter. i told my husband, that our daughter won't be over there very much, because i don't like the lack of rules. She lets them play on the stairs, and to me that's a huge hazard, and something that I can't knowingly let me daughter there.
My husband won't talk to her about it, because he says, she won't change. So to me that's fine, i just won't have any of our children over there very much at all. Plus I feel she is playing favorites. My daughter is only 6 months, but has only stayed at her grandma's for a few hours twice, but his son used to stay over all the time when he was a baby. and now, she buys gifts for his son all the time, and nothing for my daughter. Not that I am keeping tabs on everything, but I had grandparents that favored us, and it really did a lot of damage to my family growing up, and won't let that happen to my family.
I think if she isn't going to follow the rules, and do things as they should be done, then she shouldn't get to see the kids that much. If your husband won't say anything to her, then tell him that your son can't be with her.