Two 30 minute interviews
They are normally very subject based
School organised mock interviews
No.
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.
2 interviews, each with 2 interviewers. One maths and biology, one chemistry and biology. Each interview was about 30 minutes. Both were problem solving and answering questions.
First interview was very much biology based, however, it did have some Chemistry elements to it also. The second interview was based on the topic of biological proteins and the Maths questions after this were linked to this. A cross perspective is definitely needed.
Several
No.