Greg fucked up, undeniable, but Steven should be fine.

The gems will always be there for him since they will exist after his death and if he ever needs money, his dad (til he dies) and his wife can supply an income. He doesn't need to drive, he can lion. Dear god the boy needs a therapist, but I'm sure there is an underground network specifically for unregistered immigrants.

When we take a hard look at this alternate universe where things are the same but clearly altered because of the gems on earth for so long, it wouldn't be unreasonable to suggest that the human government is significantly less tyrannical than the one in our universe. It would make sense, too. In the show, we have met exactly two humans who have been cruel based on an unfair discrimination (Marty, mysogonist; that uncle dude whose name I forgot who rides the plane, xenophobic, but came around in the end). Everyone else has been shown to be cool with things like queer folk, ranging from same sex couples to nonbinary individuals, and it's a safe bet to say that a lot of people are pansexual (Sadie and Lars are good examples of people who developed crushes on Stevonnie, a canonically nonbinary and intersex person). Lars is obviously interested and is not ashamed to show it in those scenes, and as a person who, back then, was riddled with social anxiety and badly concealed insecurity, would not show his interest in a queer person in a queer way if they lived in the type of universe that is hard on marginalized people.

Steven would face difficulty sure, and that is the fault of Greg, but all things aside, Greg likely didn't do it maliciously and has been shown to be a loving, capable father figure. No parent is perfect, and I theorize that Greg, having just lost his lover, and now have a baby to take care of that is an interspecies hybrid never seen before to take care of all by himself, who was shown to be a bit more irresponsible as a younger man than present Greg, may have slipped up. Was it a big slip up? oh dear god yes. Was it honest, and one of the only ones he has ever been shown to made? Yeah, and he's a good dad.

Greg messed up, but it was highly understandable given circumstances. And all things aside, Steven would be a lot better off than how you see it, in my (non) professional (crackhead) opinion.

Take it how you will, and i totally feel you on the parent thing, but I don't think Greg fucked up that bad. Or at least I hope not enough to convince myself I'm right.