http://www.wklaw.com/areas-violent-crimes.html
If they were charged with voluntary manslaughter the maximum would be 11 years. If they were charged with involuntary manslaughter (which I believe would apply here if they went down this road if the hitting were considered a misdemeanor and there was no specific intent to kill) the maximum would be 4 years.
I'm not sure how early they could get off but it could be much less than that depending on how California's parole system works.
do not forget that they may be charged with aggravated assault on the one that survived
also, what about prior criminal history
well they were out looking for trouble and found it