I'd go for something with a large rear kids area where you could just take out the bunks or couch and put another bed in. I have such a beast although it's likely too small but is a good example. The extra 1/2 bath up in the main bedroom would be particularly helpful in their situation.
https://lakeshore-rv.com/hideout/308bhds
The back area just has a cushion bed/couch on the floor which could easily be taken out and a more traditional bed put in its place - the top bunk above the couch just swings up out of the way. I've often joked with my wife that when the kids are grown I'm going to take the bed out and put a recliner in their room and make it my man cave on wheels.