Oral history
Multiple interviewers or participants
With more than one interviewer, one could focus on asking the questions and the other could be responsible for the recording equipment and the administrative elements. Be sure to let the interviewee know how many people to expect.
Having more than one participant, especially if they are already friends or acquaintances, can be useful as it may make the interviewees less nervous. The conversation may flow more naturally, with both participants contributing and expanding on or clarifying what each other are saying.
Bear in mind this may make the recording slightly harder to follow, as people may talk over each other and each speaker will need to be identified in the summary or the transcript.