Once he had fallen a felon ran up with his skateboard raised above his head for a death blow and caught a deliberate shot by Kyle. Clear self-defense.
The second felon grabbed the sling pulling the muzzle into his mid-section and then yanked which pulled the trigger against Kyle's finger in the loop. Accidental discharge.
The third perp, a convicted sex offender of children, ran towards Kyle with a loaded Glock pointed at his head. Clear self-defense.
I realize that the system in that area is tilted against Kyle but I doubt that bias extends to juror pools of regular folks. Overcharging the young man may be deliberate and perhaps the prosecutor is actually hoping a jury would maybe assign lesser charges if that is allowed in Wisconsin.