Hi Carolyn, My husband and son are divers so here are a couple dive companies to checkout...
My son got his dive master certification with St. Thomas Dive Center summer of 2016... They are located at Bolongo Bay.
https://www.stthomasdivecenter.com/ The company they typically go out diving with now is Red Hook Dive Center.
https://www.redhookdivecenter.com/ I suggest your son takes a look at their websites... And call each one to see what company he feels more comfortable going out with.
I'm sure you're aware, August is hurricane season, best to have trip insurance!
Wish you an incredible trip!