Sounds pretty much the same as when I was a kid - We had 5 onboard (3 kids - 2 boys and a girl) for extended periods (a month or 2). 27 Foot boat. No aft
cabin and no 1/4 berths. Parents in the
Saloon (drop down table), 2 kids in the forecabin and me Brother in the
cockpit (under canvas!)....that was mainly because he snored like a pig
In latter years dropped down to just the 2 boys, so I had the forecabin to self.
Private space? that was a drawer

Obviously
women changing needed to be accomadated (apparently not so keen on wandering around in only socks

), but that simply a matter of logistics.
How did it turn out? Early on very well

, but in the latter (teenage) years I f#ggin hated being stuck on the goddam boat

But I figure that is pretty normal - IMO any teenage kid happy to be stuck 24/7 away from the world / freinds has a few problems - or will have a few..........
The nightly changeover not really a problem (albeit we weren't making overnight passages). In your shoes I would look for Mum & Dad to claim the Saloon - and one kid at each end of the boat (probably the girl in the forecabin).......or buy a bigger boat