Also, see if your hotel can set up a private snorkelling excursion, or a sailboat trip to an remote island or beach. It won't be cheap, but would be pretty cool.
I doubt that your daughters are going to be that interested in Mayan Ruins, so I would skip that. Xel Ha is a tourist trap waste of time.
The Cenote's are kind of cool, but would get pretty boring after 10 minutes to pre-teen girls. Hopefully there are some cute american preteen boys at your hotel that they can follow around and giggle at. Then you can sit back and refer to my first post.