Actually ! It's been a long time since I last! Read it so I'm not sure but Zephyr and Top aren't really mentioned in IMYM, right? I'm kind of curious as to how it'd be like if they were though? (If you don't know they're Ink's canonical parents / father figures :>) I imagine that tehy would not be very happy with Nightmare.
They were not. Although I did have ideas.
I remembered that Zephyr and Top existed too late into writing. I didn't want to rewrite several chapters. But if I didn't forget them, they would've first appeared in chapter 7 when Dream begins his search for Ink. He would've told them what happened and had their help in trying to find them.
The more important role is through chapters 22 and 23. After Dream, Epic, and Fresh saved Ink (now Ribbon) and took him to the hospital, either Dream or Core would've contacted Zephyr and Top about finding him. Ribbon fights back and insists they're evil and trying to manipulate him like every other character who isn't Nightmare or the MTT. However, they have more luck in calming him down than Dream and Blue. They even get him to think somewhat critically and realize they're trying to help and love him.
And that's where Nightmare has a problem.
What would've happened is that Nightmare captured them before taking Ribbon back from the hospital. He locked them in his dungeon (like their son) and went on a long monolouge about what his plan is. Not only that, but he took the journel he had been writing in throughout the story and purposefully read the most gruesome entries to them, making a huge point out of Ink being alone and scared. Then he killed both of them either from stabbing or beheading.
After that, then Nightmare would return to retrieve Ribbon and the events would play out the same. The only difference was be that he's proud of himself for getting rid of another person who could've taken away his little doll. And he never would've told him what happened, just encouraging him to forget Zephyr and Top existed.
I'm not sure if it's a spoiler, but this version would also lead to a variation in the ending where Ribbon would feel horrible and guilty because he blames himself for killing his parents, along with killing his friends. Even if it wasn't really his fault.