Hi!
The cohort I believe is around 50 people that they take.
The hardest campus to get into is Montgomery their cut off is usually a 7.6/8 points but you usually want even higher while the other campuses are a little less competitive. I'm not sure exactly which one is the easiest, I've heard Kingwood is less competitive.
From what I know they will only look at the highest of your two Anatomy scores so I wouldn't worry about the B!
You can rank all campuses in your application with 1 being your number one choice all the way through. So, yes you can apply to all! You don't have to rank all if you are not willing to attend a certain campus you wil not number it on the application.
I hope this helps!