Apart from the trust and corruption points, there are some very early triggers to get into a relationship with them. Rachel (the redhead) is the first after a visit to the cinema, Liza is second after visiting a restaurant, Bella follows later (depending on whether you pursue her submissive or love route), as well as Susan (who has a route involving Discreet Inc. and a pure romance route).
I'm trying to earn Trust, Corruption and Romance/Pregnancy with all 4. I don't know what routes they are but I've played lots of VNs and usually you don't receive Corruption or Lust without Trust/Friendship. They don't allow themselves to Open Up thus you're Fucked (or Not). I'm trying to make myself as irresistible as possible. I may have accidentally downloaded a Censored version (lots of ass, pussy fucking lesbian and squirting) but a "roommate/landlady" feel as opposed to familial. Now I have the .23 and they're calling each other mother and sister. Rachel/Ariel (Little Mermaid 18+). Wonderful red hair. Started 3rd and Proper playthrough (Incest of course). Fucking Amazing Pervert(eer)!!! I'll have to financially re-imburse you when it becomes feasible.