Which of the trolls knew each other in person before the game session?

Vriska knew Equius

Aradia knew Sollux

Eridan knew Feferi

If you are counting Flarp then:

Vriska knew Eridan

Vriska, Terezi, Aradia, and Nepeta knew each other.

I’m sure I’m forgetting some but that’s all I can remember. Feel free to add any I missed.

~Mod T