Honeymoon cancelled due to husband’s ex

On a routine basis, most likely that is true. But there can be court ordered, or negotiated limitations on a parent's ability to take a child out of state or to allow anyone else to take the child out of state without permission. I assumed the ex wife had something like that in place if she's able to disallow it.

OP, if you don't believe this to be the case have FI check with his lawyer.

I get it, but this isn’t really about what’s legally allowed (we've traveled with her multiple times internationally over the years, including times when my parents were also with us.) it’s more about the fact that mom is choosing the honeymoon as the first time to conveniently have an issue with it

The Ex has no obligations to meet your parents. You just got married. Give her time to cool off and adjust, it kind of makes sense she wouldn't want to help accommodate your honeymoon even if it's not for mature reasons. The best thing you can do at this point is be kind to her and continue to build trust so hopefully she does feel safe down the road to meet your parents, etc. It's her child as much as his, not wanting her to travel with people the mom has never met isn't unreasonable.

Like some have said, the ex is not required to meet or get to know your parents if she doesn't want to. That's her choice to make. When it comes to these issues, your husband and the ex need to stick to the agreed upon parenting plan. I am a child of divorced parents and my sister is as well. Unfortunately, she got the rougher end with a dad whose mission in life at the time was to make our mom miserable. It happens. Good for your husband getting comfortable with her step dads parents. That was a commendable choice your husband made, doesn't mean she is required to do the same.

There isn't really much you can do about it. Just treat your step-daughter as if she was your own, don't talk bad about her mom within ear shot, and believe your husband and the ex are trying to do what they feel is best for their daughter (even if you may not agree).

I would suggest consulting with a lawyer. My cousin ran into this issue with his daughter (from a previous marriage) when he had to work abroad for several months. His new wife planned to fly out with his daughter, then her parents would fly back with her and deliver her to her mother, so the new wife could stay longer with my cousin before flying back. The ex threw a fit about it (completely out of spite). They sought legal counsel and it was determined that since the child was in the care of the father at that time, he got to determine who he felt was safe for his child to be around; just as the mother had the same right during her time with the child. It would be worth a phone consult with a lawyer to determine your options. Plus, it sounds like you and FH will want to know your rights going forward anyway, in the event the ex tries to pull this sorta thing again in the future.