Legal Question in Criminal Law in California

Yes. But whether you can legally shoot either of the attackers is another question.

People are allowed to resist an attack with an amount of force that reasonably seems necessary under the circumstances. Sometimes shooting an attacker is reasonable. Sometimes it isn't. It depends on the facts.

In your hypothetical, the second attacker is also armed. That makes it more likely that shooting him would be justified. But I can imagine situations where it wouldn't be.

Yes. If both armed, and they attacked you, you can fire away, until you are out of danger.

Yes, there is in the law a right of justified self defense in an emergency that overcomes most 'anti gun' and age rules. Even convicted felons would be entitled to pick up the gun and use it if so justified, even though they are prohibited by law from 'possessing' a firearm normally.