I'm with Brandye. You just have to be firm about the rules in your household. I do think there's an aspect of moving back and forth that lets kids feel they can just walk out and leave their chores behind them - get away with it because when it's time to go, it's time to go - and then they just sort of get that new mindset that they don't have to do stuff. I think it's a huge problem when you're talking consistency, which is the stuff of good structure and parenting.
The other problem may just be transition stress. If we had to move back and forth as often as our kids do, it would be stressful. I never knew exactly how stressful until I started living back and forth between D and my home, before we finally made it permanent. My younger daughter always had a harder time of it than her older sister - just personal differences - and it was hell for a day every time she came home.
Some of the things that worked at my house:
Gave my daughter some "down time" when she got home - quiet play and nothing at all that would up the anxiety or the wildness quotient.
Talk about the transition issues BEFORE they leave. Acknowledge that it is hard, and that everyone will be happy if we try to get back to normal faster. Discuss ways of getting there - ask for their input. Making it their problem too helped a lot in my household.
Remind them on the phone, before they come home, that everyone is going to be working as a team to have a nice "reunion." Maybe create a ritual together (some fun thing) that you all love that you can do on transition days to ease the transition. In our house, it was often an art project - good occupational therapy anyway. Maybe in your house it will be tkaing a walk, having ice cream, whatever. Something to make coming home seem like a good thing.
Anyway, good luck. This is a toughy.