Also if this was just about me I would pass but I would like my kids to know their cousins so this is why I am trying to figure out a way to make it work.

Hi. This is OP. Surprise surprise I received an email saying my kids are now invited. I am now trying to figure out if we can go as we now have made other plans and would have to back out. I am sort of proud of myself for finally standing up to our family drama but wish this had happened a few weeks back when I wouldn't have had other plans.

OP: This is rather more complicated than it looks at first glance. It is not a weekend away from the kids since you will be around other people's kids. So its not an adult get away. It depends on how close you are with your aunts DD. Will she and you be terribly hurt if you do not attend the wedding?
As for the cousins, it sounds like you have extended yourself financially and in other ways to have your DC's be friends with their cousins. And the cousins probably cried poverty/ no baby sitter as their exception for bringing their kids. If having it right in front of you is going to cause you to rethink the relationship/ have resentment, then send regrets. People are very often not only not grateful, but actually resentful when you help them financially, so the cousins could possibly not care much about your feelings.
I think it is interesting that your DH right away said, don't go. That makes me wonder if he sees the relationship with the cousins in a different light than you do.
My feelings would be hurt by this mainly because you feel that the closeness of the cousins is not reciprocal and that always hurts.
I do not see how the time has passed to ask about bringing your kids when the wedding is a month away. But I can see how your aunt may have felt pressured and just said no more kids!