After I interview a teacher, should I show the interview transcript to our editor first or give it to the interviewed teacher for verification first?

Of course, show it to the interviewee first.

Out of respect for the interviewee, you may hope that the interviewee can provide modifications to the manuscript. The editor has decision-making power over the manuscript, but the interviewee does not. If you show it to the editor first, and after the editor approves it, the interviewee then proposes revisions. After the revision, you have to go to the editor again, and maybe the editor will reject the manuscript this time. In other words, if the editor does not approve it, it will be useless no matter how much the interviewee likes your manuscript.