All of what follows is one man's opinion. I'm somewhat knowledgable about these matters, but others are far more experienced than I.
I agree wholeheartedly with the notion of a shotgun
generally being the preferable tool for what you're talking about.
Hallways shouldn't be an issue for a couple of reasons:
1. (The less important of the two, IMO) Any shotgun designed for defensive purposes is quite maneuverable, with double-barreled "coach guns" being even easier to move around.
2. Whether it's you, your dad, your mom, your grandmother - it doesn't matter, none of you should be moving around the house if you think there's an intruder around. You should call 911 and stay put, with whatever firearm you've chosen to buy.
And if you were to buy a shotgun, I would lean toward a 20 gauge, as it is sufficient for the task you'd be putting it to, but less punishing on an older person who needed to use it.
I would also be fairly wary of the idea that a shotgun is that much easier to shoot than a handgun. You might have a few inches margin of error, but in order to take full advantage of what a shotgun does, shot placement is almost as important as it is with any other firearm.
All of that said, in your particular situation, with people around who aren't likely to get much training or practice, a four inch .357 Magnum revolver loaded with .38 Special or .38 Spl +P ammunition would be your best choice. A Ruger Security Six can still be had at a reasonable price, and unless you start shooting full house magnum loads with serious regularity, it will likely outlive all of you, and get passed on to a future generation.
Or you might go with the tried and true phased plasma rifle in the 40 watt range.