I've been watching the Net for over a decade. Before that, I had access to a database not open to the public that listed fatal shootings and also non fatal ones.
In all that time, I've seen no report of a private citizen running a standard capacity shotgun empty when defending self and family. None.
What does matter much more than bells,whistles,tuck and roll upholstery, fuzzy dice,CD player,hold the mayo,is expertise,practice,and a shotgun/load that's appropriate to the mission and shooter.
For non shotgunners, no shotgun is a good idea. For those willing to get out and practice, practically any reliable shotgun they can shoot in comfort and effectively is a good choice.
For those of spritely build, the smaller shotguns in smaller gauges make sense, but as has been said, lighter shotguns kick more, all else equal.
A 20 gauge weighing 6 lbs shooting an oz load with the same balance and fit as a 12 gauge weighing 7 lbs shooting 1 1/8 oz will feel harder kicking, not the intended opposite.
If all the folks who will be shooting this can handle a fairly light 12 gauge, that may be the better choice because of the wider range of models and the plethora of ammo. The 7/8 oz loads out there now for the 12 are close to optimum for trainng new shooters, and lots of fun for all.
Best idea so far, try out different shotguns and pick the one Mrs or MS Rabbi prefers...