You need to get 2 courage to do Eckhart's heart scenes and 3 charm to do heart scene 3 with Kara. There's also an extra relationship point bonus for having Academics 3 in heart scene 3 with Amy.
There's also an extra relationship point with Sara you can get by having at least charm 2 in heart scene 3, but like if you're already going for charm for Kara, you will already meet this requirement.
It's pretty easy to level your stats by just doing every work shift and watching every movie in the movie theater, and like occasionally going to the library for academics on the weekends.