You will get your share of the pool and beach at Ixchel. Great location and access. The clubs are primarily there for people without direct access to a good beach and / or the desire for chairs, beds, umbrellas, towels, food. We stayed on the far south end of the island with just an okay beach so the clubs helped. All of the beaches in Isla are public but the clubs provide for all of the amenities without you having to deal with anything, except a cost. Most all of them cater to families. With a couple of teenagers and for a change of pace Kin Ha may be up your alley - rope swing, kayaks, snorkeling (although that may not be up your alley). Our teens had a good time there. https://kinhaislamujeres.com/
As other posters note, get a cart for at least a day to explore. It's fun and a great way to get around the island.
There really isn't a way to see the whale sharks unless you're up for the 3-hour (round trip) boat ride. And, even then, you still have to get in the water and swim with them to really see and get their full impact.
Just want to reiterate the rooftop of the Secreto as a place to go see the sunset.