First of all, what an unfortunate series of events. I'm very sorry to hear about such a tragedy. Obviously, there are lots of facts not in this question, but generally speaking, if a charge of Involuntary Manslaughter is brought the resulting penalty (if convicted or plead out) will likely be something greater than parole.
Your best friend really needs to be represented by a competent criminal defense attorney. These are extremely serious charges.
Disclaimer: This answer is given for discussion and informational purposes only - it does not constitute legal advice and no attorney-client relationship is formed. If you are in need of legal advice or assistance you should contact a professional in your area.
First of all, your friend doesn't want parole... because he'd have to be sentenced to prison first.
Parole is supervised release after someone has served part of a state prison sentence. Inmates get time off for good behavior and are released on parole. If they violate the terms of their parole, they can be sent back to prison for up to a year at a time.
Unlike parole, probation can only happen BEFORE a person goes to prison. In a felony case, the defendant can get up to a year in jail as one of the conditions of probation. If you complete probation successfully, you don't go to prison; if you violate probation, the judge may send you to prison.
DUI causing death can be charged under several different Penal Code sections, with punishment ranging from a year in jail to ten years in prison.
If your friend can't afford to hire his own attorney, the judge will appoint the Public Defender to represent him.