Regarding the "not all the trolls met in real-life" bit, and disregarding the fact that they all came together on the meteor, the first time Aradia met Sollux I believe is when he killed her. Also, Equius and Vriska were indeed neighbours, and Eridan and Feferi worked together to kill lusii for Gl'bgolyb to eat so it wouldn't Glub. Most of the trolls lived nowhere near each other (Tavros lived in the middle of the desert, while Kanaya lived in an oasis in another desert), just like the kids.