Soldier Boy.      

Call my lawyer and get in line, punk.

Don't think it didn't occur to me. But no.

For one thing, Soldier Boy can't fly and isn't nearly as strong or tough as they are. So he's clearly not their daddy.

Besides, whatever I come up with is almost certainly going to end up in my published fiction, so Soldier Boy (and other characters belonging to someone else) are right out.

A current street-level tabletop superhero game I'm in has as its setting a world where, a couple of decades back,  a city was destroyed by a bungled attempt at stopping a supervillain, turning public sentiment against the "capes" and causing the modern world to be bereft of superpowered individuals, at least publicly.

The heroes are brought together, invited to the funeral of a well-known millionaire philanthropist, only to find that he had been a "cape" and had maneuvered circumstances to bring a group of superpowered indivividuals together to help the city in its hour of darkness.

The clincher? To make sure of it, he'd fathered every single one of the characters, using genetic manipulation to ensure they would express powers. So the PCs are all half-siblings!

Maybe that can provide some inspiration for you.

Heh. Back when the Global Guardians universe was still a going concern, I toyed with submitting a proposal for a game. Prineville (set in the town of the same name in central Oregon).

The backstory (which none of the PCs would have known at the outset) was that there was a super who could manipulate DNA--his own as well as other peoples'. He could shapeshift his appearance easily, but making deeper, more substantive changes (acquiring new powers) was delicate, dangerous work. He could as easily kill himself as give himself nifty powers since he was doing it by trial and error.

So...he settled in a small town (the eponymous Prineville, OR) and began to use the locals as test subjects. Either by masquerading as various husbands and impregnating their wives, or while performing medical procedures on likely candidates, he would father a townfull of kids who all had carefully crafted changes to their genetic code. In effect, he bred a townfull of kids who were (as the campaign began) just beginning to discover that they had superpowers.

Of course, they were living in a town with a well-established history of a very high level of birth defects, miscarriages and stillbirths--the results of early experiments, before the villain refined his technique and understanding. Nobody knew why, though it had been investigated thoroughly and Prineville had been the subject of tabloid attention for a while. Contaminated environment? Radiation? Meteor Rocks?

Best of all, when the inevitable PC romances blossomed, they would eventually discover that they were all...half-siblings.

Eventually I came to my sense and decided the heavy editorial hand of the GGU PTB was more trouble than I would be willing to put with, so I shelved the idea. But it may yet see the light of day as fiction.