Group interviews, which thankfully I have only had very few over the last 20 years, turns into a he said/she said report.
Normally my “group” interviews were from neighbors or ex-spouses having someone sit in with them. I learned a long time ago to be upfront and ask for one spokesperson, then remind the non-spokesperson that helping is cheating. At the end, I always ask the non-spokesperson if there were significant errors or missing issues in the interview – I have never had anyone say yes.
As for the group interview where the investigator “spills” your secrets – that is not how an interview is conducted. We don’t tell folks anything but our names and the privacy act with perhaps a mild humor story to put them at ease.
I suspect that your coworkers know more about you than you realize. This is often the case when I do interviews.