I believe ZA & KK to be very credible. I also believe that EN was truthful both in his conversation with ZA and KK, and in his statement to Mogg. The story as relayed by ZA & KK is so very similar to the story EN told Mogg, I think we can mostly take EN's statements as true. He probably got some of the details not quite right -- that's to be expected from anybody.
But the bare-bones facts as EN saw them? I tend to believe that he was telling the truth: i.e., he had gotten threats to himself, his mother and his baby sister; he was at the park; he saw the green car; he thought it was the people who were after him; he called his friend with the Audi; the green car chased them; he fired at the green car; he was shocked when they saw the green car pass by very close to EN's own house; they went into the cul de sac and he fired at a person at the car and at a person running from the car to the house. I believe those things happened.
EN, however, can't tell us what TM, KM & BM were doing or thinking prior to all of this. If there were driving lessons at the school, EN didn't recognize them as such when he saw the green car. If there was a road rage, EN wasn't present for it. If there was a spiky-haired dude, EN doesn't know him. EN doesn't know whether BM was in the house sleeping or playing xbox.
For those things, we have to rely on the words of known liars and on any physical evidence that might be available. Surveillance footage, phone & text records, any other witnesses, etc.
I'm convinced that we correctly know what EN saw, what he thought, and what he did.
I'm also convinced that the Meyerses are still not being truthful.
I'd bet money that it was that Stan -- but not very much.