Nice picture; good story. Thank you for sharing.
I'm wondering whether the photo is reversed, a mirror image of the original. The buttons on the coats and vests, and even the breast pocket of the coat, seem "backwards" to modern eyes. But I don't know if men's clothing all buttoned on the same side back then, or not. I've never noticed one way or the other before, and I'm not home so I can't go peruse original photos in all my books I'm going to get around to reading someday!
But if it's flipped, they'd both be holding their revolvers in the left hand. But maybe that makes sense for an old cavalry officer, and like father, like son?