A stepmother who is prepared for her SD to go to NYC instead of her, with her DH, while she holds the fort at home, and people are calling her selfish and jealous? Seriously, get a grip. I once had a stepmother call me up to tell me, "you are not a member of this family. This family consists of me, my husband, and our children. It's not convenient for you to visit this year." It wasn't personal, either, because she barely knew me and I lived in another continent. She just hated that she wasn't my father's first wife. She wasn't his last, nor even his second to last, either, so in fairness her stress was well founded, but shame she chose the prior kids as her target, eh. THAT is a shitty stepmother! (She was a psychiatric social worker, too. So no claim to lack comprehension of the effects of her choices.)
Someone in a cash strapped family, with three very young children, has been fine with her DH taking an adult SD to NYC for 4 days as a solo father/daughter trip, from family money while she does all childcare... and you think she's mean and jealous and unreasonable This adult stepdaughter is applying to be adopted, OP, if yours isn't happy! Fucking hell, you sound amazing to me. And if your kids are bad sleepers, and your toddler is a handful and the older two squabble a lot, then I am sending you a Katniss salute right now.
I completely get why you're stressed and angry about this. You agreed to a sacrifice to benefit him and his daughter, with all the costs to you and no plusses at all, and he's laughing at you when you find the agreed time away didn't factor in travel. That's not great.
Definitely agreed on the making life simple while he's away; I'd stock up on cheap frozen pizzas and fish fingers and not worry about healthy home cooked food for those days if the kids are hard work at this age. I think they vary so much and some people's kids would be no bother, while others would be hellions. Screens too, I'd relax restrictions on. And I'd discuss a clear arrangement whereby you get to go away and leave the kids with him the following weekend (friends or family further away) so you can have some me time, too. Though hardly going to be NYC, is it.
Incidentally... this veteran stepchild thanks you. You sound a good one to me.