It really depends on your relationship with them and what you are hoping to get out of having them with you on vacation. We have cruised with 2 different friends. The first ones we had staterooms next to each other and had a BLAST!!! Our kids were 3,3,5 and 5. We spent the majority of our time together. We have been friends since 3rd grade and know each other very well. Next cruise with different friends. We were on deck 7, they deck 2. We were WAY to close to each other. Newer friends, didn't lay out expectations ahead of time....BIG mistake!
January 2004 we will be cruising with my inlaws. We are on deck 8 and they deck 7 both very close to the stairs for kids now 9 and almost 11 to easily access grandma and grandpa. If my kids were much younger I would be very nervous about them going to their grandparents room unescorted unless it was just a couple doors down.
One thing we are doing is having a vacation planning meeting this Sunday to go over what we are planning on doing during the cruise. I know they will do some things with us and prefer not to do others. I also know that DS and DD will want to spend alone time with grandparents.
Go with what you feel is right. And remember to plan alone time. I love my mother dearly. I vacationed in Norway with her for 11 days. 24/7 for 11 days had me going nuts by the end of the trip! Also remember it is a VACATION!!! A time to relax and rejuvinate, it should not be a time to be stressed out!!!
Good luck with what you decide.
Amy