A couple of answers......
It would be difficult to swim laps in the Solarium pool as it is not that large. Google some pictures of Solstice, and you will see.
As for adults only, when we were on Connie earlier this year, a couple with childern did go into the solarium area and start using both the T-pool as wel as the hot tubs.
Being the bad guy I am, I notified an officer, and they were spoken to and left. I have no qualms about doing that. Adults only means adults only. Celebrity could put up more visible signage to that effect aslo.