We were just on a liveaboard and a doctor(diver) suggested that instead of Sudafed, my buddy should try Afrin(nasal spray) instead. His opinion was that Sudafed causes a slight swelling in the ear canals which can lead to ear problems.
Note that Turtle "Farm" and Turtle "Reef" are two different locations. Turtle Farm is a working turtle farm(shorebased) while Turtle Reef is the other Divetech location. It's a good shallow dive with a 35' mini-wall 50 yds. offshore. Kneeling on the sand just past it, I managed to hit 59'.
As mentioned, it's a healthy drive from where you're staying, especially through Georgetown, try to do it on a day there's no cruiseships in town. Or go really early as they tender everyone in after anchoring around 8AM in so at 7-7:30 GT is a ghost town.
Eden Rock would be another shallow option, we couldn't get below 40' there, but the reef has been pretty beat up by years of cruise ship divers. Good facilities and easy entry.
Sunset House would be a good dive also, your wife could have lunch at My Bar and also view the Cathy Church photo gallery onsite. No beach though just ironshore. You and the kids can get pictures with the mermaid (Amphitrite) at 53'. It's well marked and just offshore.
The only shoredive/beach combo I know of on GC is Cemetary Beach. It's on the north end of 7MB. Never dove there though.
Understand that what makes 7MB such a good beach makes it lousy for diving and most of the rest of the westside is ironshore down to the water.
I also liked Aquarium as a shallow boat dive. It's only about 45' to the bottom of the sand channels between the reef. It's also possible in a lot of locations to stay on top of the wall so your max depth is between 60-90' even if others go deeper. Peter's Reef is another shallow site with some decent diving between the coral fingers.