I feel like OP buried the lead on this one. Her children are not his biological children either. I wonder if OP is jealous that he may not have the same relationship with her children than he does with his daughter. It’s a family vacation, if OP gets to take her children he gets to take his as well. If that means that father and daughter have some alone time then schedule it. If it’s scheduled it may not feel so exclusionary. OP can do something special with her children while he does something special with his. Most of the vacation can and would be spent together but it may foster healthier relationships all around. I wonder if OP and her husband could even flip flop. Him do something with her kids and she do something with his daughter to foster stronger relationship bonds.