My sister is having a casual birthday party cookout for my nephew at her house. I asked her if I could bring my sister-in-law's 2 kids to the party, they are going to be coming to stay from out of town. My sister said this was fine. When I told my sister-in-law we could take the kids for the weekend she said the whole family would come visit and come to the party. This would add to more adults and a baby. What should I do? should I talk to my sister or my sister-in-law? What should I say?