As I recall from my Ayoob, the law on self-defense against groups generally says that if an individual in the group isn't making themselves scarce immediately on the commencement of hostilities by their group mates, they are a legitimate target. The defender isn't required to decide who is merely along for the ride and who is driving (so to speak).
The family claims Mieses was trying to get the others to stop when the driver decided safety required him to go, which is tough for Mieses but he chose to break the law by riding at all, much less riding with thugs.
