I would discourage the idea of a left-handed guitar for a couple of reasons.

First of all, just as a general principle, you never see any left-handed pianos, violins, flutes, etc. If your son learns to play a left-handed guitar, then his guitar would be the only one he could play. There are not that many left-handed guitars out there. Should he find himself someplace without his guitar and someone offers him a guitar to play, he couldn't use it. He'd be stuck. Bad.

Second, in learning the guitar, the most difficult hand to learn to use is the left. It requires more nimbleness and dexterity to finger chords, play scale passages and runs, and other such stuff than the right hand does, no matter how complex the picking patterns or arpeggios are. A "southpaw," holding the guitar the same way a right-handed guitarist does and learning to play it that way actually has an advantage over right handed people in that they are generally more deft with their left hand. That's good. Jimi Hendrix notwithstanding, you shouldn't be able to tell if a guitarist is left or right-handed just by looking at them.

Left-handed guitar? Not a good idea.

The whole family learning? Sounds like a great idea!! Happy picking!

Don Firth