Obviously, no prequel will be made because of time and money constraints. A prequel would obviously be about a younger Vander, Silco, and Benzo. But usually there would also be at least a fourth member in the gang. Who should that fourth member be?

Ekko's dad? He's still alive in game, so this begs the question where is/was he in the show.

Finn's dad? Silco said Finn was leeching off his legacy. Given Finn's age, his das was probably more likely a mentor to Vander's gang rather a member.

Vi and Powder's dad? We saw their mom a few times but not their dad at all.

Huck? I prefer Vander helped him because he helps everyone in Zaun not because he's an old friend. It would make his downfall extra tragic.

Mylo and Claggor's dad(s)? Make them bio brothers like Vi and Powder were bio sisters. It would explain why Vander adopted the boys after he had already adopted the girls. I think the brothers got short shrift in the show. This is my favorite option.

Sevika? A younger tagalong to a three older folks... sounds familiar. It would provide another reason why she has such animosity towards Jinx. My second favorite option.