how about testing some away time before committing to a whole week? that way, you'll have a better idea of how your sister, the boys, and you and your hubby cope. maybe an extended sleepover is in order? 3 days, perhaps? you never know, the boys might have such a blast that they look forward to the next sleepover, and you can go and have fun with hubby knowing they are also happy and having fun.
I think if you have someone reliable to watch them, esp your sister and kids are fine with her, you should go. Kids are our life and we do everything for them, BUT you also need some hubby & you time, just to relax & rejuvenate. I like SGC's suggestion. By the time kids get older, you may not have the energy to do the things you can do now....I say go for it!!!
I agree.