We certainly do try to help all members of a family as individuals! Generally I think you'd be better off with the smaller operators. Depending where you're staying, you could also consider Belize Academy of Diving (BAD only in name), who serve the hotels well north of town. At the northern end of town are a couple of small operators who will "do you proud" - Chuck 'n Robby, and Everette and Enes (I apologise that I can't for the moment recall what they call their business). And there are one or two others. At that time of the year no-one will be busy, so you'll get individual attention from operators who might not be as good for you at other times. But as it'll be quiet I wouldn't book anything in advance, but have a look around once you arrive and make your mind up then.
You say you'll be "in Belize".. All these operators are in San Pedro on Ambergris Caye - is that where you're headed?