Anon, are you me? When I saw the promotional posters for Graves and Credence, my first thought was, "Oooh, family air".

I have a bundle of notes for a fic which pretty much goes along your prompt lines but for one difference - Grindelwald finds out about their connection before Graves does, and starts toying with Credence under his father's features so he can taunt Graves with the perverseness of it. Would that be too dark for you? There wouldn't be more than what we see on screen, and the endgame would still be Graves and Credence bonding post trauma, possibly with additional Graves/Newt (my OTP).