I’m a day late on this one - take one day off CC and look what happens! - but a few things to add.
For your son: if he’s happy with this teammates, if you think his coaches are supporting him and he’s learning, if the club has experience in the college recruiting process, and if the team is as competitive or more competitive than the HS, then 100% he should stay with the club. There is zero advantage in the recruiting process to coming from a HS team, and given the relationship he already has with the coach and the success he’s having at the club, there is no reason to switch. (And yes, academics matter a ton, though there is a fairly wide range of expectations depending on the school, including many of the best rowing programs in the country.)
For your daughter: if being competitive post-high school remains a goal (she’s in eighth grade, lots of time), I’d even more strongly suggest that she optimizes for the most competitive program (assuming support, coaching, internal team mentorship, all those things). Coxswain recruiting is more heavily influenced by race results, and on the kinds of recordings that come from competitive races with top-tier crews, than rower recruiting. Assuming the club is the more competitive option, there is also a ton to learn as a coxswain, and you have many more opportunities to learn, become a student of the sport, etc. in a full-year program.
Good luck and have fun!