Let' me give you the skinny on how we do it at my school.
Your scores would be averaged.
Then we'd dissect the reviewer's comments to see what was the difference. The scenario you asked about is very common; sometimes we wonder "did interview the same person?"
If an interviewer is known as a hardass and always gives poor or weak scores, then they're typically discounted. On the other had, if said interviewer gives a high score, that says something very positive.
The same holds true for interviewers who are softies, a bad score from them gets our attention right away.
Whether a student or a faculty member gives the review is weighed less; we tend to trust our student interviewers.
Keep in mind that at MD schools, they have to whittle down the applicant pool somehow, even at the interview level.