Hi
yhk3887,
the short answer to your first question is:
no, both interviewers don't need to say "yes" for a candidate to get accepted.
The short answer to your second question is:
it depends.
It is always up to the AdCom to decide. And it's not as black and white as "yes" or "no". First, for the overall rating, interviewers have to select 1 out of 5 options, so there is some granularity.
Second, interviewers must submit a full report where they have to type the answers to many questions. In my personal experience as an interviewer, my reports have always been 4-5 pages long.
So, the AdCom has a lot more information to assess a candidate than a simple "yes" or "no". So, even if an interviewer has selected a negative overall rating, the AdCom will still read the entire interview report and judge by themselves whether the negative rating is justified.
I hope this clarifies a bit.
Good luck!
Warm regards
Alex