Aquatic Adventures in Dewey, Culebra (Taz and Ann at 515-290-2310) can do a group of 6-8. Ten might be too many.
They will take you to two different sites in a day, and also feed you lunch.

We dove and snorkeled with them in August.

Their Dive Shop is right above the Dingy Dock. Same building.

On the web they go as diveculebra.com