Hey there, don't know if it's too late, but I interviewed with Harvard last year (and was accepted).
The interview is not meant to trip you up - Dr. Brendel and Brooke wanted to know a bit about me (I have a non-traditional history as a student), why I was attracted to Harvard, and what I wanted to do with the degree. Really straight forward.
Feel free to DM me if you want to discuss more.
I'd also like to join the Slack group. Got an email back in February saying they were forwarding my name to the committee... and now am anxiously waiting for whatever comes next.