I'm not going to extend a specific invitation to two nieces for an annual family event that everyone is invited to
That's very specific... Would your nieces be upset about not getting invited?
It's alright, the other people in our family calls them cockroaches.
Intentionally excluding family members to a gathering is rude, but sometimes its best to do so to avoid any family drama. They ones excluded may be hurt and further distance themselves from the family. If they ask why they were excluded, be honest so that they know their behavior is unacceptable.
It's alright. They'll be fine. They should worry about how I'm going to treat them when they go to university since they will be the one who will be in debt.
I believe you should try to be a little nicer to them even if there was past drama. Don't you want your family to be stable? How about letting them come to this event, maybe you'll make up!