I have never dove with Pro Dive but we go to Coz at least twice a year to dive. There are lots of excellent dive ops that with 7 divers will give you your own boat. In fact with 7 it may be much cheaper to just charter your own. Dive with Martin used to charge 400 for a 2 dive charter and include the rental gear if needed. I would imagine other ops would be in the same range. Tres Pelicanos continually gets great reviews on this site, I have not dove with them but no reason not to check them out. My favorites are Aldora(for the huge tanks) Dive With Martin, Blue Magic, and Christy with Blue XTSea is a huge supporter of this forum and appears to run a top notch valet operation.
Most ops are excellent with email replies. Contact several and find the one that is right for you. Make sure they know you have 7 divers and where you are staying.
Main Differences will be cost (60 to 100 depending on # of dives) # of people on a boat, departure point, # of boats available, tank size, site selection procedure, cash discount, surface interval location, ascent protocol (set time, as a group based on lowest air, with a buddy) and "valet" service where the op handles, rinses, stores, and transports your gear. Ask the questions, include your expectations, and you will find the right dive op that fits your needs. Anything with more than 8 divers on a boat would be a no-go for me.
The biggest factor I see will be that all 7 divers are at the same level of ability. The op will have to choose dives for the lowest level of skill or split the group by ability unless everyone agrees to dive at that level. Keep in mind there are no bad dives in Coz. The shallower drifts are actually my favorites. Except for deep swim throughs at Columbia Pinnacles, I'd rather stay at 40 feet for an hour and a half.
Good luck,,safe travels.
Jay