None of the above.
Unless they're content to sit at the beach/pool on Little Cayman they'll probably be bored, it's a pretty small, quiet island. If it matters, LC is mostly boat diving also. fwiw, I've never been there but friends have. They like it a lot but even they admit it's really quiet.
We've dove on Grand Cayman before and my sisters family - 3 adults, 1 teen were just there over the holidays. They all found enough to entertain themselves while my brother-in-law dove. So that might be an equally pricey option...
Bonaire is excellent shore diving but none (literally) of the shore dive sites other than the resorts have any facilities. Most don't even have a decent beach. Or shade, water or restrooms. So not good if the non-divers wanted to follow along.
There's a few nightspots in town but it's generally pretty quiet by about 10pm most nights. There's also cruise ships in now - they dock at Town Pier. I'd want to be somewhere else when they did. One ship is probably 1/4 of the population of Bonaire. There's a small shopping district, wind/kitesurfing at Lac Bay and kayaking in the Mangroves.
Very few of the resorts even have a decent beach - just Plaza Resort, Eden Beach(marginal) or Harbour Village (pricey) The rest and most of the waterfront condos are on ironshore - the few that aren't usually mention it.
www.infobonaire.com is a good starting point if you haven't already seen it.
With 3/4 non-divers Richard's suggestion is a good one - look at Curacao instead.
Much more to do there, nightlife, famous shopping district downtown, about a dozen casinos - an equal number of good clubs, better beaches, more of them, and at most you can dive while they play on the beach as most beaches are also the better dive sites along the coast. It's the same reef so almost the same diving as Bonaire also. Just a little farther out in some areas. But that's actually better since you walk in off a sandy beach instead of climbing over ironshore.
Compare the entries here:
http://www.shorediving.com/Earth/ABC/index.htm
Almost every beach has an on-site beach operator, most also have a dive operator and many have a snack bar also. Quite a few have all three. Also there's the Dive Bus, they do escorted shore diving/snorkeling all over the island. And will pick you up at any resort in town. You will drive more to dive on Curacao than Bonaire, sites are farther apart - most require a 10min. drive in from the main road bisecting the island. Get a good map or GPS also.
It should be easier/quicker to get to from your area than Bonaire also, esp. thru MIA. A lot of the Bonaire connections are thru Curacao.
Curacao Travel- Caribbean, Curacao, Dutch Caribbean has details on everything.