Each kid in a single bed - don’t bother with a sleeping bag.
Other than disposable pads and some form of absorbent underwear (we won’t call them diapers), try to keep this a
s normal as possible. And easy on you. This is a vacation, even for mothers. (Laundry - well that job never ends, even on vacation. I have done a lot of laundry on
DCL - and I am single.)
Dress him in his pajamas in the bathroom or behind the curtain that separates the double bed from the singles.
Maybe your kids won’t pick on him if they understand this is not a failure on his part. The majority of us have some quirky aspect; they can start learning empathy within the family. (sorry if that sounds like a lecture. I don’t know how my parents handled my issue so that my siblings didn’t ridicule me. Actually, I don’t think ridiculing occurred about most things).
I can’t remember if it’s the alarm or having someone wake me and take me to the bathroom that is the mechanism that retrains the brain. Perhaps a little research on which has better results will steer you in the right direction.
And if the alarm wakes everyone for a few nights, it night be worth it for a lifetime of “normalcy.”