I'm not going to allow any of my ex's side of the family to come to my son's birthday party
Why don't you want your ex's family there?
The family is too large and I don't like them.
Just because the family is large and you don't like them, doesn't mean you should disappoint your child by not having them there. It's rude to exclude them.
Thanks for the advice but I don't care.
I'm just saying that your ex has a right to bring his family around his own son.