it would definitely help if DH's family is more familiar with him. That isnt impossible. About the playpen, is it the kind like a foldable cot with mesh on the sides? Over here, they call it the travel bed. Perhaps try and use all his normal beddings, etc, from home so that it is familiar to him. Stay calm and let him feel that you are confident that it will be ok. Perhaps do a trial run by staying over at their place for a weekend.
I do agree that flexibility is an important key to feeling sane. We, too, are confined to do all by ourselves as we cant find babysitters at all. We only ever tried a nap at a friend's unplanned and it actually went well!
hugsss and good luck!