Relationships chaos

Yeah, the game doesn't do a very good job with step relations like this. It's kind of like the Brady Bunch syndrome -- Greg and Marsha should have been able to date when they were old enough (technically), but not while their parents were married to each other because, ewww. Okay not exactly that because they did grow up together as step-siblings, but had they been older when their parents married then the restriction would have made no sense.

The only way I know to play through that is to engage the feature of an NRaas mod that we are not allowed to mention by name here. It begins with a "W" and you could post at NRaas to get more information as needed. :)