You're saying using a firearm to shoot them would be justified? This example is where I'm hung up on that it wouldn't as neither are armed.
This is my opinion only, not a lawyer or a judge, and I don't speak for anyone or any organization I may or may not work for:
Having said that, off duty two thugs try to jump me together I'm going to plug them both.
The legal concept is disparity of force. Maybe it's just one on one? Does that mean you can't shoot him? I dunno.
Can you articulate he was 4" and 60lbs bigger than you? What if he's the same size but you're 63 and he's 23? No such thing as fair.
The trick to keeping yourself on the right side of the law is having a damn good reason and explaining the fuck out of it, with your attorney guiding you.
I'd be shocked at a self defense shooting against two attackers, armed or not, resulting in charges for the shooter.
Unless you're some dumb shit mall ninja and tell them during the interview you've been training to be an assassin since you finished the Vince Flynn novels and this was the chance you were waiting for.
But again, not getting jumped at all is better than explaining why you had to shoot a couple wannabe robbers.