This is very country (not as much office) dependent. However, the typical format is that you have 4 final round interviews with Associate Principals, Partners and/or Senior Partners (formerly Directors). The 4 final round interviews are conducted on the same day 95% of the time. If there is a real shortage of APs and Partners, they may only conduct 3 interviews. If they can’t even schedule 3 interviews with APs and Partners, they may ask you to come back for another interview. This is not usually a sign that they need “another read”. This is also usually only the case if you are locally based. If you are traveling for the interview and they have a shortage of APs and Partners, they likely ask you to reschedule.
All of the APs and Partners don't need to say YES for you to get an offer. It helps but if there is a NO or even two NOs, you need to have a really strong YES advocate (the more senior the better) in the decision meeting. The decision meeting is not a vote. Basically, all of your scores have been put into a database from all rounds and are displayed on a screen for all of the final round interviewers to see. The leader of the decision meeting asks for someone to "make the case for" and then someone to "make the case against". Everyone listens to both sides and then there is a discussion before ultimately a consensus is ageed upon.