I think they'd prefer to be at home, BUT I don't think I'd like having them in their crates for most of the time. I know your FIL said he'd come let them out and stay for an hour and come over several times a day but that is still a LOT of time for a big dog to be cooped up.

There's no way you could take your pups to your sister's with you? Or your FIL couldn't take them home with him for a few days? Is there a professional dog/pet sitter in your area you could try out?