Post-divorce relationships and meeting/getting to know the family

OP, you just need to be friendly, polite, civil, considerate, etc. You don't need to be besties. It's fine.

I'd let the cousins thing go. It would be weird and drama-ish for you to "call her out" on it.

I kinda get what you are saying in some way, though. I have been dating my "boyfriend" for lack of a better word for six years. Living together for four. He has two teenage kids to whom I am a quasi-stepmom. I do worry the lack of permanence is not great for the kids. Your bro's arguments about college financial aid are solid, btw. That's one of the reasons we are not marrying, at least not yet. I have enough assets to kick them out of the running for financial aid, but not enough to hand over the extra cash they would need thanks to my assets and income being included on their financial aid forms. I think it's pretty awful to marry someone, make it so that their kids can't get financial aid, and then NOT help pay for college. A lot of my assets are in a family business so it's complicated. It's just easier not to get married from a financial messiness standard but the lack of permanence and commitment is a little weird feeling.