Totally feel your pain, we we have been in the same boat for many years. My kids, 16 and 9, detest sharing a bed. It's not even about being opposite genders, they just accuse the other of kicking, being generally restless, and stealing the covers. And DH is far too clingy to ever agree to share with one of them instead of me, lol!
I've also oscillated on how accommodating I'm willing to be for their pickiness. I mean, when I was growing up, travelling always meant that me, my older brother, and younger sister were all going to be sharing one bed. And back then, it was always a double instead of a queen. It never even occurred to me to complain about it, that's just how it was. So, maybe they're a little spoiled. But, like many of you have mentioned, when they don't sleep well, everyone is miserable and suffers.
I usually spend (i.e. waste) a lot of time before trips searching for options that involve three separate sleeping options, but most of the time I can't find it and we just end up bringing an air mattress. I always ask at check in if they have rollaways, but more often than not, they don't. The most recent on we have been using is this one:
https://www.walmart.com/ip/Coleman-QuickBed-Lite-Slim-Twin-Skinny-Airbed-White/40703442
It is very small and lightweight, and we have no problem flying with it, even when we are only bringing carry-ons. It's reasonably comfortable - DS actually complains less about this one than some of the bulkier ones we have used in the past.