There are caveats to almost everything I'm about to say...
Threesomes are not INHERENTLY bad--IF they are experienced enough to keep track of ALL other members of the team. That's not the situation in your case.
Solo diving is not inherently bad, either--IF the diver is experienced, well-trained (are you rescue diver certified?) and well-equipped. Do you have a full range of solo gear complete with TOTALLY redundant air supplies, etc? If you are not trained for solo, then it's a bad idea.
Partnering with very young divers in general isn't a bad idea--AS LONG AS they can operate as a fully functional dive partner. That means can they not only handle their own safety, but can they handle YOURS? In other words, can this young person rescue a full grown partner including surface tows, etc...? If their size or skill level prevents this, then you are, essentially, diving solo with someone in tow. (see above about diving solo.)
An relatively inexperienced dad with two inexperienced teens? No caveat here...not an ideal situation at all. The suggestion to round out the dive team with a guide is a good one. Not only would there be another adult, but a well-trained one at that. In addition, just about everyone involved would benefit from what a guide could show you. These ops know the reefs well. They dive them every day and can show you more in minutes than you could discover in a series of dives on your own.
With time, your young ones will mature, develop and acquire experience and training. They will become good partners with time and patience. Don't rush it. Hopefully, there will be many more trips for ya'll to enjoy.