BV is supposed to be 2 rolls, regardless of the number of combatants - one person takes lead, everyone else contributes helping dice, and everyone suffers the same injury, regardless of individual weapons.
For alternatives, you could try hacking in the Mouse Guard/Torchbearer conflict system, or just run a series of versus rolls between opponents. If you do either of those, you’ll probably want to keep in mind the Series of Tests rule for advancement.