1) 12 choose 4 to separate off the first session

2) 8 choose 4 to split the second and third sessions

3) 4 choose 2 to get the first two contestants from the first session

4) 4 choose 2 " " " second session

5) 4 choose 2 " " " third session

6) out of 6 remaining peeps, we need 3 from any, so 6 choose 3 for the last contestants

All of these things must happen at the same time so multiply. See how I approached that?