Wedding with infant

So destination wedding.....the bride and groom want my husband to be best man and they been talking about it for months. Said baby and I are welcome blah blah blah got rooms figured out. Seems good to go.

Get their invitation in mail says reception is adult only. How you supposed to get a sitter at a destination wedding? Husband is thinking of stepping drown as best man. This is very expensive to go to (hotel, plane tickets) pretty much eats up our vacation fund and said if his family can’t go he won’t go. They literally been talking about this for months. Are they being passive aggressive and saying I need to stay in hotel in strange city with baby and we just want the husband there? Thoughts? Is it okay if husband steps down?