This is one of those situations so often discussed here ... you come on an incident in the middle; HOW do you decide who the good guys are, and who are the baddies? Who do you shoot first? How do you explain why you got involved with a weapon to your jury?
Get through or turn around, get to safety and call the cops!! They get paid to sort out messes like the one you described.
"The gun has been called the great equalizer ... It insures that the people are the equal of their government whenever that government forgets that it is servant and not master of the governed." --Ronald Reagan