a) In "normal" families, it is basically a Grave Social Don't, if you haven't had direct experience of their Problematic Behavior, not to visit for, say, Official Holidays. So basically, I'd go the once, mostly so you can be supportive of your husband, but also so you can experience some Behavior (because there likely will be some) and then not go again. (Unless your husband wants the support.)

b) Continue to encourage boundaries, while being supportive of his decisions: Good.

c) Do bring up the money worries -- like, once. But then don't harp on it. Just, have a reasonable discussion about the worries, so that it can be on the table, and if it comes up again once they start in on it, then it won't be a Shocking Surprise.