Lock them in a room while you're taking boxes out of the house... and back in at the new place. My Yorkie freaked out and went missing for 8 hours (at night).
I would limit their access in the new house, and try to keep to the exact same schedule they're on now. Maybe set up a daytime room like the kitchen, and if they sleep with you, allow them in the bedroom at night.
Keep them on a leash when you introduce them to the yard. Pay attention to any spots that attract their attention and make sure they cannot escape. And watch them closely the first few times you turn them loose in the yard.
Good luck with the move...