Could be that a 6 & 5 y.o is just too much of a handful for them simultaneously... It doesn't have to be all ominous and sinister.
Geez.
I like the idea of having the 5y.o staying for a long weekend, I know my daughter didn't want to be gone a full week yet at that age.
I agree that its best to explain how you and hubby discipline and outline their routines.
In all honesty my child has never stuck to her routine when gone from home, the idea is her aunts are spoiling her, so yeah, cranky tired, sugar loaded child is what I used to get.
Lol never thought I'd say its so much easier now that she's 13.
Also encourage your 6y.o to report any kind of spanking, if you call her and she does report such an incident, you get your butt down there and collect her, and then obviously don't send your son. Ever