The odds are no different if the cadets are selected without any regard to their school.
The odds can be significantly different if they cadets are assessed relative to each school. ie:
School Applicants Places % Chance of success
FTE 1000 24 2.4%
CTC 1000 24 2.4%
Oxford 1300 24 1.8%
What Libertine said about 24 per school was what I heard from Oxford last year. So if anyone knows 100% the policy (rather than what they think), it would be appreciated...