on lieu of the pregnancy ask, I have two bits to ask:
What if y/n is like, really really excited to have a kid? (And possibly was told they couldn't have any... But monsters, ya know?)
My family can't go on birth control because it makes us crazy. I mean the added chemicals to our body literally mess with our brains and we go kinda rabid. So... That... May not work.
Nightmare would soften up considerably if you're genuinely excited to have a kid. The guy has a soft spot (that he absolutely LOATHES) for babies and very young children, so even though he very well COULD stop you, he'll let you have this. He actually insists on fathering it, too, if you're so sure you want to keep it. Not because he wants to be a dad or anything, he just wants it fully loyal to him (a human/monster crossbreed is a powerful asset), and what better way to secure loyalty than with a familial relationship?
Killer isn't thrilled, he's always seen himself as more of a cool uncle than a father, so maybe he could just be that? Sure he'll help you out, but he's not gonna want to be a doting/super involved parent. He thinks it would be best if the kid didn't know about their relation to him if it ended up being his.
Dust doesn't gaf you're raising that thing on your own. At MOST he'll get you what you need, but he's still pretty hands-off regardless of how excited you are.
Axe is willing to be hands-on and help out, if only to get closer to you. He's not super thrilled about the idea of fatherhood, but he has fancied the idea in one or two daydreams. Maybe the idea of a teeny him does appeal to him, the more he thinks about it. Someone he can teach to hunt and fish and survive. Maybe it would be nice to have legacy that's not completely fucked up. But still, it starts as a ploy to earn your favor by stepping up and helping.
Cross is wishing so hard he's the father. There's only a small reluctant part of him that's upset this happened here of all places, and not on a cute cozy little farm that he's been dreaming about sharing with you. Even if he's not related to your child, he's going to step up the most out of the others and love them like his own. He doesn't know when he'll get the chance to be a dad otherwise.
Error is worse than Dust. You've got a whole posse of guys willing to help, so you definitely don't need him to raise your little abomination. He's out. Maybe he'll check back in fifteen years or so, see if the kid holds any potential (if it's his, that is. If it's not, he doesn't care at all).
As for the birth control thing? Easy. Nightmare's got that covered. Everyone gets a chastity belt.