My Husband isn't on my side

It has caused quiet a stir at my husband's side for not inviting my SIL at my LO's Birthday. My husband is feeling the guilt trip from his mother, that he told me it was wrong. We shouldn't be like his sister. Because the kids like to play with each other. I'm not having none of it though and told him his mother needs to stay out of it, she's causing a row. It's not our fault his sister acts like stupid-ignorant-child and treats my child indifferent and I'm supposed to take it??

By the looks of it, she doesn't care if the cousins have a relationship or not, her husband told me point blank before my child was born that it's not necessary for cousins to be close while I was looking forward to it. She can't even bring herself to say she's my child's aunt. In fact, my niece does facetime with their family friends-kids but never once have called to check up on mine. My husband says, I see too much what they're doing instead of focusing on what's right for us. I don't know if he's this stupid or just trying to be against me. Apparently I'm the wrong one here because I'm choosing the higher road and don't want nothing to do with them.