M.P.
Stop looking at the arrangement as help. It's bonding time for your children and their grandparents. Obviously it's not helping you. It's making life more difficult because of your feelings.
You can change your feelings by changing the way you look at it. Instead of telling yourself you hate it, tell yourself it's good for the kids. Stop with the negative thoughts until the positive ones become true.
I suggest you rearrange your schedule so you do have something to do while they're gone. Use the time you were using to do those things to do things with your children. The best of both worlds.