-How much boat are you gonna rent? Seven people and six sets of dive gear requires much boat.
-Do you know the water off Marathon? Getting out to the reef line can be kinda tricky in places. Scars on sea grass beds are not cool.
-Good water ebbs and flows off the Keys. Operators talk to each other... as do locals.
-How many dives are you planning a day? Two or three? That means 12-18 tank rentals plus gear plus seven people in a boat.
-Don't forget you gotta hump all 12-18 tanks from the boat to the car for fills.
-Will you have O2, first aid kit, a tag line, and dive flag on board your rental?
That being said, it does rock having one's own boat.
Use Tilden's Scuba Center to dive.... rent a boat to explore a day or two.
Have a great trip.