scheduling issues

so I posted earlier about SO traveling for 16 days every three weeks. My dilemma is what to do about my 3 kids. I was thinking about what if I could get 1 full week off during that time... have you ever heard of that? I could work Sun Mon the week he leaves (he leaves on Tuesdays comes back 2 weeks later on Thursday) be off the following week, then work Fri, Sat the following week. During the next 3 weeks I could be on the regular schedule. Or, would it be better to go to a PRN schedule? How does that work? Can you decline to come in when they call? How many hours does one typically work in a week on a PRN basis? I'm a new nurse, going to be off orientation soon, and I can do the thing where the kids' grandma keeps them while I work for awhile, but after a few months, that won't be possible anymore. Secondly SO and I are planning marriage and having a baby in the next year to 18 months which would REALLY pose a problem for child care, as my kids grandma is my ex MIL. She won't be keeping a new baby I've had with my new husband. Is the schedule where I'm off a full week in the middle of that and work 24 hours for the week before and after really outlandish? I know we are fairly overstaffed now with all the new hires, so I don't know. What do you think?