I try and rotate couples as best I can. I RARELY, if EVER pair adults with their kids unless its a private class, and even then I'll try and bring along a DM to be the kid's buddy, in addition to a DM to help with the other aspects of the class. I've found, as a general rule (yes, there are exceptions, I'm sure) that personal relationships bring baggage that doesn't belong in the ocean.
My thought is that you had better pray your buddy is exactly as good as you are at every skill. What if the dominant person has a catastrophic event underwater? The more submissive diver then has to save the day, without getting himself/herself killed in the process.
In my Kayak Diver course, I am always certain to include: "You know, they call tandem kayaks 'Divorce Boats' for a reason..."
As for a well-intentioned, but "just certified" beginner trying to teach family how to dive (even just the "beginning stuff") I respectfully assert that that is a VERY bad idea.
During our first year of law school, our deans/profs stressed that, at that stage, we didn't even know what we didn't know, so attempting to dispense our newly learned knowledge was certainly a very very bad idea.
The same applies here. No disrespect intended, but it is my honest opinion.
Now, I question how you're getting access to the gear you use to teach your family the basics. What shop would rent you gear and tanks for students when you're not an instructor? My answer: A shop that doesn't want to say in business very long, should a tragedy occur (and I pray it doesn't).
If you're just letting them use your gear, how are you in a position to slow a too-fast ascent, since you're not wearing gear? Where is your reg to give the student if he can't find his on the reg recovery drill?
Assuming you're just letting the student use your gear, you will be modelling bad behavior in a few ways. First, you're basically teaching the student how to solo dive, and that's bad for beginners. Second, you're teaching the student to shoot to the surface when bad things happen, rather than look to a buddy who has gear to share.
Just my two cents.