What are your in-law's reasons for wanting the kids at all and for wanting them separately? It doesn't sound good to me. If it were me, I wouldn't send my kids to stay with the grandparents alone at all. Why would you want to? Spanking? Excuse me? Why? No thank you grandma and grandpa Scrooge! The fact that your kids come home unhappy shows they do not treat them well. Red Flag alert!