If you're looking for harem content, you'll either have to play the corruption route or wait until the game is complete for romantic harem, if Neon decides to do it. The game is meant to be more realistic and grounded in that sense, just fyi. But, some of the LIs will be ok with sharing if that counts
The incest is for romance route for sure, maybe corruption route too, haven't played that yet (probably looking forward to the most actually). Basically, if money or blackmail are involved rather than love or force, it's probably the corruption route.
You know, I haven't seen that specific scene myself, but bouncing off your description, I wonder if Ashe purposefully hit Wren with her car. They were young and we don't know the details after all. Could be that Wren doesn't even know that. Would also inform why she doesn't mind MC driving fast in the car (accident = fear + regret, purpose = just regret), though you could easily chalk that up to time and moving on. I've never taken sleeping pills, so I don't know what they're supposed to be like, and certainly not when mixing with alcohol, but if her state of mind is affected in the morning by them, and she did hit Wren on purpose, perhaps she's projecting herself onto MC in that moment. Just something fun to think about.
And about Nicki, I think that's just supposed to be her personality. She seems easy to push around, slow to hate, and quick to forgive. At least when it comes to MC.