Compass Point and the East End might be kind of quiet for two teenage boys. There's just not a lot out thee to do. Good boat diving with Ocean Frontiers on-site - my buddy dives with them..
Lighthouse Point is about 10mins. from anything. As Kathy mentioned, you'll need a car. Their shore dive starts shallow off their dock and you can swim out to the main wall drop-off from there.
I'd look at Coconut Bay condos also, it's near Turtle Reef which is an easy, shallow dive. Macabuca is there for lunch and Cracked Conch for better meals. Almost across the street is the Turtle Farm/Boatswains Beach attraction.
You might also look at Hepp's condos - a smaller complex also north of SMB. They have a ladder they deploy for guests to access the Hepp's Wall and Arch sites but it's a decent swim out. I see the condos on vrbo.
North SMB is pretty quiet south to about the Ritz then it gets more congested to downtown. Lots of condos in that area but no diving off the beach - the reef is too far out. Most of the dive operations pick up there - boats are often at one of two marinas a few minutes away. Ours even dropped us for lunch between dives.
Stingray City is 15' deep. You're the rays best friend till the squid is gone. It's a lot more fun than it sounds like. One of Psycho's (moray) descendants lives in the patch reef nearby - otherwise it's a lot of sand. Our dive was called at 45min.
Georgetown can have multiple cruise ships in daily so best to avoid that mornings. There's a few good restaurants worth the drive. Also Eden Rock/Devils Grotto are two shallower shore dives with the cruise port 50 yds. away. They're the 4pm dive when the cruisers are queueing up to leave.
And further south is Sunset House, Walk-in's welcome. There's 2-3 dives there - a small wreck at arpimd 70' and the Mermaid stature in about 60' and the tourist sub goes by in the mornings. Also the Cathy Church photo school/gallery and My Bar is a good place for lunch. Two easy entries to the reef there - off the dock or the saltwater pool, open to the ocean on one end.
Still further south is Smith's Cove, a public beach with a shallow dive. Rent tanks at Eden Rock or Diver's Supply as there's no facilities there.
I'm suggesting all these shore dives as with 4 divers you're looking at 2 tanks/$100 each for boat dives so that will get pricey fast. Definitely worth it though - as others mentioned, usually first dives are deep followed by a shallow 2nd dive. The water off the North Wall is often stunningly clear - some operations warn you to watch your computer as you drop as there's no particles in the water for reference.
Some boat dives to ask about - Big Tunnels (deep) Orange Canyon, Trinity Caves. If you stay at Lighthouse,. Divetech goes to Ghost Mountain - arguably one of the best but the swim through is deeper. Aquarium on the west side was among the better shallow dives.
Scuba Diving Videos, Guide to Best Grand Cayman Dive Sites lists over 300 sites - many with videos.
Also the Kittiwake is a dive cleaned wreck that all can do. The first couple levels are open with access cut into the sides. It's so shallow it's even a snorkel - a recent storm tore the wheelhouse roof off. Most shops dive it by appt. so call around to find one that fits your plans.
You might also look for one of the smaller operators - usually their boats are bigger anyway and they limit trips to 6-8 divers max - with 4 you'd have some input on site selection. Try Wall to Wall, Ambassador Divers, Neptune's Divers or Stingray Watersports at Coconut Bay - the owner also owns a rental condo.