Generally, the interviews are conducted by two people (faculty/student). Each interviewer also explained that there are cases where a third interview is granted, but that only occurs if the two interviewers differ significantly in their evaluation of your performance. This is, of course, very rare so don't sweat it.
UB has a great program and new, exciting things coming in the future (new medical school location in downtown, etc.). Also, if you're interested in topics in biomedical ethics or come with a humanities background like me, the curriculum includes electives where the more abstract aspects of medicine are explored.
Good luck and don't be nervous!