Remember this advice isn't official. There is no guarantee it will reflect your experience because university applications can change between years. Check the official Cambridge and Oxford websites for more accurate information on this year's application format and the required tests.
Also, someone else's experience may not reflect your own. Most interviews are more like conversations than tests and like, any conversation, they are quite interactive.
Number of interviews: 2
Skype interview: No
Time between each interview: 1 day
Length of interviews: 20 minutes each
There were no personal questions whatsoever; each interview consisted of 10 minutes with each of the two
Each time, they would talk to me about the diagram/graph and what it told you about something, and they would then ask a question applying what they had just said.
I just did a couple of past papers a few days before.
I prepared by just revising the A level course, although in hindsight this wasn't that important in terms of knowing information, more about keeping your subject intuition fresh.
My expectation was that there would be lots of classic questions about my personal statement and why I wanted to come here, but there were actually none. If I had known what the interview was like, I'd actually conclude that there's not much you can do to prepare!
It is clear that the interviewers are looking for insight into your internal thought process.