I suspect Gerard Keay was descended from Jonah Magnus (kinda) and that's why he was so good at KNOWING and surviving until the Von Closen family cancer (eyes developing inside him, in this case as a "brain tumor) took him out.
TMA doesn't touch too much on the mingling of sex and horror (use protection or you might catch worms), but it's not unreasonable to believe more people than Tim were having sex (the Lukas family continued, after all) and there is simply NO WAY that Jonah was unaware that Mary Keay's mother was a descendant of the Von Closens as she worked part time at the Institute.
I suspect he had an affair with her mother, and when her husband found out he took his own life. Mary was a born sociopath (Jonah already had those tendencies), and he would have LOVED running an experiment to see how Mary would develop largely left to her own devices. How much of her was HIS?
And this means, of course, that GERARD was his, after a fashion. Of course Jonah let Eric Delano go, sure, tend to his descendant...only Mary didn't have a nurturing bone in her body and she certainly wasn't going to have a disabled husband that couldn't feed her information from what she considered to be her birthright.
Jonah knew exactly who Gerard was, just as he knew who Mary was. And of COURSE he let Gerard wander around the Institute with Gertrude...Gerry BELONGED there (and he was covered in eye tattoos around Gertrude, who had always been so careful to REMOVE eyes from her vicinity so that Elias couldn't watch her...but she couldn't exactly do that with Gerry's tattoos, now could she?), he was so good at KNOWING. Jonah might have even considered WEARING him one day (finally a ginger!).
But of course, Gerry died...and Jonah likely KNEW he had the "tumor". Might have even tried to recover the body, if Gertrude hadn't "mutilated" it and effectively put the morgue on lockdown.
We know the Lukas family concerned themselves with legacy, even the Fairchilds were a loose group of a family. I don't believe Jonah was immune to that idea, even if he used his "family" more as an experiment.