It would depend on what was being said and how. If I had time between my car and there's I would probably call the cops and say there is a possible kidnapping and run to assist with the cops still on the line.
If I had followed C earlier then A
If I had not then A,C
I would probably not pull my firearm just because I would rather defuse the situation by all other means neccessary than escalate it, again this is from my standpoint.
Only A if she attempts to hit you with her car, and I would rather disable the car and not risk hitting the child.
Never B, if your injured then you won't be able to calm the father down. Plus, I'd rather not be run over with a 1-2 ton vehicle, I hear it can cause serious bodily harm.
C is a good one if she isn't willing to be erratic while driving. You can follow and give dirrections to the police if they are willing to help.
And as for the following, this is why it is best to get the cops there as fast as possible.
Again, this is from my point of view. Everyone else would react differently, that is what makes us humans.