Imo, if the jury follows the letter of the law this will never be M2 and certainly not Manslaughter.
There are way too many premeditated acts done by the driver and the murderer.
1. Suspect opens fire at a first location. No one fired back per EN. The very first location shows he had an intent to harm even though he knew they were not returning fire.
2. Continued to pursue the vehicle even though it backed up turned around and tried to make it back to the safety of the victim's home.
3. DA and EN came right to the property and home of the victim.... opening fire for the second time killing Tammy Myers and had intentions of killing Brandon. The guy with the beard per EN.
4. EN admitted that he came there to kill. Even boasted that he had killed those kids.
Once the driver and EN continued to pursue the fleeing vehicle.... going to their property with the full intentions of murdering them it became as premeditated as it gets. EN became the hunter and the victim became his prey.
Let's take a step back as I think you're making certain assumptions without actually realizing that you're making those assumptions. This quote may also help you in that previously on here you've made the distinction between legal gun owners having a right to bear arms to protect themselves versus felons illegally carrying guns, which it turns out that EN - just like BM - is a legal registered gun owner who has a right to arm himself for protection:
Police said they are looking for at least one more suspect, but they believe Nowsch was the shooter. Homicide Capt. Chris Tomaino told reporters that he owned registered firearms but wouldn't say how many guns or what type of weapons they were.
http://www.cnn.com/2015/02/19/us/las-vegas-road-rage-killing/
Now with that out of the way...
#1 - As a gun owner you have a right to using your gun for self-defense, which self-defense doesn't only apply after you've been shot at and are lucky enough to have not been killed or incapacitated after the first round is fired at you. Also with self-defense it doesn't require actual danger, but the appearance of imminent danger "Actual danger is not necessary to justify a killing in self-defense. A person has a right to defend from apparent danger to the same extent as he would from actual danger." We know BM had a gun and was in a car that was pursuing EN and EN said he saw a gun flashed at him (which BM could have done without realizing it because he was afraid), EN had a legal right to use his gun in self-defense for the perceived threat of an armed car chasing after him after flashing a gun at him. Consider the scenario of the tables were turned - if BM/TM had just been parked by the school and EN/DA came up behind them and flashed a gun at TM/BM and then after that kept pursuing them in their armed car, would BM/TM have had a right to self-defense under the imminent threat of an armed car chasing them that had just flashed a gun at them?
#2 - This actually is an assumption made, but nowhere in the record is it stated that EN directed the car he was in to go there nor his purpose for going there while at the same time it has been stated by sources across the board that EN didn't know whose car the Buick was, so he wouldn't know that the owners of the Buick live on Mt Shasta. This is a very critical point because the extent of planning into going it depends where on the spectrum it falls. The closest area that EN is premeditated to wanting to go is telling Andrews that he wants to go home. For all we know he did exactly the same thing as TM did after the alleged fear of harm from the death threat where after going by home he then went to be sure that the threating car wasn't near his home, which I don't think you'd say TM for going to her home was in the process of attempting M1. Any number of times you'll hear about trials where someone gets acquitted of M1 where the jurors themselves will say they thought the suspect guilty but acquitted because the DA didn't provide enough evidence - the proof has to sustain that they actually did what they were accused of rather than a gut feeling suspicion to get an M1.
#3 - On this I agree in the sense that he was responding to bare fear rather than imminent fear, which does not justify what he did but instead would make it M2 or Manslaughter.
#4 - Actually he didn't. He said what he did once he saw them and his boast was actually admitting to what he did in response to bare fear and even if he did that doesn't necessarily make it M1. Reverse the situation and instead have it be where TM/BA found the alleged road rager who threatened the lives of the Meyers family and they followed this car home where they shot and killed that person on the bare fear that the road rager was in the process of getting guns to carry out his death threat on their family. Killing the road rager in his driveway wouldn't be justifiable homicide, but instead it would be M2 or Manslaughter as the Meyers would have over-reacted to provocation where they used lethal force in the presence of mere bare fear. In that situation TM just as well could have said "I got those road ragers, they were after me, but I got them," which such a statement wouldn't be admitting to M1.
EN had a legal right to call 911.
EN had a legal right to go home or to another home or even to the police station.
He did not have any legal right to pursue someone who was trying their best to get away from him. That is simply hunting someone down in order to kill them which is M1 and that is what he tried to do by his own admission and succeeded with TM.
Virtually everything you said is exactly the same position the Meyers were in, yet I do not see you supporting charges against them. It's not like someone who could be charged with attempted murder would lie to the police about what they were doing, so you cannot assume that just because the Meyers didn't confess that they weren't lying to the police. The Meyers had a legal right to call 911 and a legal right to stay home or even go to a police station and they pursued someone who tried to get away from them, which make their pursuit illegal and them hunting someone down. We just have to trust that someone who has done all those things you list wasn't attempting murder because they didn't confess to the police they were in an attempted murder plot. To be clear I'm not saying the Meyers were in an attempted murder plot, just using this as an example to show how similarly the two groups operated and where differences come is by assuming people who do all these things are being honest to the police.
The intent to kill in this case is glaringly obvious. That was his intent and he tried his best to carry it out.
Intending to kill is not the same thing as M1. Negligently killing someone by accident is Involuntary Manslaughter and no one is saying that this was accidental negligence. Intending to kill someone itself isn't a crime at as it depends on why and under what circumstances you were attempting to kill.
I suspect since Andrews wasn't the shooter his lawyer will try to do a plea deal in exchange for his testimony in court against EN.
It would not surprise me if Andrews turns states evidence or at least has been trying to reach an agreement on a deal.