She hasn’t always hated them. Their relationship has dramatically diminished over the last 10 years. Her siblings are difficult people and were jerks about my brother’s wedding. But I like my cousins and want them there. My mom actually threatened to not come if her siblings are there.
My fiancé thinks my mom should be the one that's tells her siblings why their kids (my cousins) are invited but they are not. That it is her issue with them and not mine.
A few additional facts that might be relevant. We are having a destination wedding (so 3 days of opportunities for drama) and my mom is gifting us a lot of money for the wedding.
What should I do?