I'm going to recommend not diving with Fosters. First of all they're in Georgetown. If the cruise ships are in port (almost daily), that's a zoo - the streets are crowded when they all get dumped off their ships simultaneously and most are oblivious to the fact that cars are coming from the opposite direction. Second Foster's takes 18-24 divers max per boat - check their website.
Eden Rock was pretty tired looking several years ago. Being a short walk from the cruise port doesn't help. We thought that was the worst dive we did in a week of diving. But it is shallow.
Sunset House was good, there's a lot of good diving in less than 60'. Their signature dive, the Amphitrite Mermaid is 55' at the base. They're in South Georgetown.
Another option north of 7MB would be Turtle Reef. It's a good vertical wall that was about 45-55' to the sand IIRC. Lots of interesting stuff going down the wall starting at about 25'. The older kids can cross the Sand and get out to the wall if you let them. During the day Tarpon schooled in one area in the shade. It's a shortcut to the North Wall so watch for larger pelagics overhead out in the channel. I saw some Eagle Rays go streaking overhead. Easy entry via a ladder also. Sun Divers is on-site there for tank/gear rental as needed.
Aquarium is a shallow boat dive. Some areas were 48-50' to the sand. Lots of sand channels and coral heads - look for the tiny fluorescent blue/orange cleaner shrimp, they'll trim your cuticles. Governor's Reef was another dive that could be done shallow - I don't remember more about it. Most 1st dives on a two tank trip the operators typically go deep unless you ask otherwise.
A better option would be one of the smaller diveops along 7MB. Neptunes, Off the Wall, Wall to Wall, Ambassador Divers, Sea Sports or Indigo Divers - among others. Most go out with 6-8 divers max. guaranteed so your group of 4 would have a lot of say in dive destination/depth. I think Ambassador is 6 max. Links to all of them are here:
Cayman Islands - Grand Cayman, Cayman Brac and Little Cayman, Travel and Tourism Site Caymancase here is Neptune's GM. C'J's also works for one of the ones I listed.
Check with them about pickup also, most run free shuttles along 7MB. If you're going to shoredive, you'll need a car as all the diving is either north of 7MB or around Georgetown - very little is shore accessible in front of 7MB - the reef is too far out. If your condo is the one I'm thinking of (near the Westin), there's no shorediving in that area. Andy's at the airport is good for cars. A couple of blocks from the airport on the left is one of the bigger markets if you're planning to cook.
btw, Stingray City is the most fun you'll have in 15' of water.