What do you do in this gift giving case??

My husband's family (mother and sibling) always complain to him about gifts. They complain if they don't get something then complain if they do! Mind you they aren't close to him mainly because the mother keeps the siblings away from him(15 & 18). She has never been to our home period and has recently allowed the son(18) and daughter(15) to come for the first time. After they were here for a little over an hour she called for them to be brought home.. They live about a 30 min drive away. While the daughter was here I took her to a store she loved it. It was her first time there and she went on and on about how cute everything was there. Her birthday came so I bought her some things from the store and sent them by my husband. She found something wrong with each thing and sent it back. For Mother's day I sent items by my husband for his mom. She took it but complained also that she didn't like it. I told my husband I WILL NOT by another gift for them. I can say that the son hasn't complained about a gift so far. I've always raised my kids to take whatever someone gives and say THANK YOU. I will not allow them to tell someone they don't like a gift. I think it is rude and ungrateful to do this. I think they just wanted money instead of a gift. His mom has always tried to get money from him since I've been married to him, even if it isn't her birthday or a holiday. Is it wrong for me to stop buying gifts for them...or should I try again?