someone with a 31FS will jump in with the exact dimensions, but looking at the pictures on jayco.com, they look the same as in our 2016 31FK.
I've got one son who's 5' 5" and has to sleep diagonally on the dinette. My oldest is now 5' 11" and has to sleep all diagonal and scrunched up on the sofa. The sofa is a jackknife.
I'd say if the kids are 5' or under, they'll be ok.