What do you mean by "allow you to kill a 3rd party"?

Like if rioters are breaking into your window and start trying to pull you out through it, then you floor it and kill someone else in the crowd who wasn't actively breaking into your car?

This is something that's going to vary from state to state, but ultimately it will be a case by case decision where a jury will decide if the use of deadly force was reasonable.

You will be judged based on other's perception of the events, not based solely whether you yourself thought you were in danger or not.

So, someone trying to "drive slowly" through a group of protesters would probably be found at fault, while a car that was stuck trying to wait patiently suddenly having a Molotov cocktail thrown on it would be judged differently. Even then they will need to consider whether you could have just gotten out of your car and run.

https://www.reuters.com/article/world/fact-check-drivers-dont-have-the-right-to-plow-through-protesters-idUSKBN23B39F/

Sure, there are some states that let you mag dump through your front door if someone rings the doorbell

I vaguely remember reading in my criminal law textbook, years back, that murder is one of the few exceptions to the doctrine of necessity (this would have been in the context of US law), so I don't think that it's ever legally-permissible to intentionally kill some random person to save yourself. IIRC the rationale was that it prevents thing like terrorist groups from coercing someone to do actions for them by threatening someone else.

That being said, there are obviously points where people are forced to take actions where either one group of people is going to die or another; in ethics, the trolley problem is a well-known example. For a maybe-less-artificial problem, closing hatches in a ship where not everyone is out of a compartment to prevent the ship from going down, say. I don't know how law applies in the situation of weighing lives; my assumption is that it doesn't mandate inaction.