For the initial two, Mike and Steph, I got inspired by a pornhub video, because I just wanted a couple to practice NSFW with. Then over time I started doing more with them.

Mike is inspired by Barney Calhoun from Half Life 2 Steph is inspired by Leela from Futurama Chris and Tara inspired by general Mean Girl x Pushover Boy shipping tropes. Etc. etc.

I'd have to really drill down on each of them to give more concrete inspirations but I tend not to think about them that hard these days, lol