I have an idea of how to possibly give them a reason to stick around, but it would require my character being introduced... I'm away from home on a phone so when I get back later I'll expand on what I'm thinking could work.

Edit: So we know a fight is coming. My idea is really just: Violet sees whoever is coming from the woods, possibly after diverting Joseph's course after seeing him use his power (depends on the obvious two factors of if [@memetrash101] is okay with a collab intro and if he's okay with one involving this) and heads to the mine with him thinking that it would make a good spot to hide in while they pass. The reason I'm giving this as a reason for Abi and Brooks to stay is that Violet is going to consider anyone with powers and/or survived the gala as a precious test subject, and would forcibly keep them around (at least for the fight, since if the people she ran from suddenly showed up, she'd try to make everyone get into the mine until they were gone/dead.) She'd also be somewhat likely to throw their truck at the enemies, so there's that. That would get everyone in one spot and stuck there until the fight was over. 

Anyway, if that's not plausible just let me know and I'll try to BS up another reason.