Most cruises have a baby sitting service or kiddie daycare

OP, maybe you should give more information about the situation (wow, this is like the lyric of a rapsong ;-)) As I understand for now, you've treated your family on a nice cruise. Probably something your sister and her boyfriend can not pay for themselves (not strange, being a family of seven). Second point, the communication/relation between you and your sister is definitely not perfect. Your sister doesn't take your well-being into account. They just dropped the kids with you and assumed you would look after them. Plus you call her boyfriend a deadbeat, so no friendly feelings for your brother-in-law either. Third point, you don't have a very good contact with your nieces. You call them bratty so I do not think you really enjoy your time with them. This is YOUR VACATION, why didn't you speak up? Also a good sister/mother (in my belief) should already noticed the absence of a bond between her children and sister. In that case she does nobody a favor when she puts you together with them, so the parents act does seem very self-centered. So my question is: Why treat your sister and family to a cruise when there doesn't really seem any respect for each other? Try to take control of your own life OP and speak up, nobody else will/can do it for you!

There's this amazing 2 letter word called No that helps in situations like this

"Time to go play with the fishes kids"

Don't be afraid to stand up for yourself. Make your free loading sister and her dead beT boyfriend take responsibility for their own kids. Don't cruise ships have day care facilities that you can put the kids in ? Good luck

Were you forced to pay for the cruise in the same manner that you were forced to watch those kids? You need to grow a backbone, OP.

I'd like a follow up, please tell us what you did with them. Did they end up in the daycare, or did you tell the parents off?

Oh that sucks! You should surprise them with the responsibility!

You could just not do it. YOu know, tell them you aren't watching their little monsters and walk into the kids free zone yourself.

You allowed it to happen.