If it's fair to assume that interviews for osteopathic schools are conducted like interviews for allopathic schools, then take comfort in knowing that with few exceptions, what you say and do will not make a tremendous impact on whether you get accepted/waitlisted or rejected.
A school will interview only those candidates who qualify for a spot in their class. So, congratulations on all of your accomplishments in making it this far. Unfortunately the schools cannot accept everyone they would like to accept, so they get together in committees and argue over whom they should accept, waitlist, and reject.
The interview is just one of several factors taken into consideration. There are all sorts of forces (many political) that sort of shape the decisions of an admissions committee. How does the interview weigh in? Basically, it gives you an opportunity to prove to them that you can engage another human being in conversation. You can prove to them that you are able to think. Some interviewers try to stress you out and some ask tough questions. I met with about thirty interviewers last year and just one of them did this to me. His colleagues had liked my application enough to offer me an interview, but there was something in there that he didn't like and he used that to create an uncomfortable interview experience. The other twenty-nine interviewers really just wanted to chat.
They will just chat with you. Some will want to know if you have done research or if you are interested in research. Some will want to know why you are interested in clinical medicine. But most of them will realize that you are nervous and that you are not a doctor yet, so they will ask you things that are really basic, like where you are from, why you like basketball, or what made you decide on medicine. That's all.
Pretend you're talking to your favorite teacher, professor, or some older family member whom you admire and respect.
If you are getting interviews now, you will certainly get into places. If anybody should have something to prove at the interview, it should be the school. So ask lots of questions about curriculum and student life. Don't try to impress anybody. Just be yourself and ask questions now, before it is May 15th and you are deciding between multiple acceptances!
Good Luck!