PG: starting PG/sub PG/sub PG
SG: starting SG/sub SG/sub SG
SF: startingSF/subSF/subSF
PF: blank/trainee 1/trainee 1
C: blank/trainee 2/trainee 2
This should ensure trainee 1 and 2 have full 48 minutes and won't leave the court unless they get injured or foul out. Play trainee 3 and 4 in the next game then 5 and 6 in the scrimmage.
That said, if anyone fouls out or gets injured during the game, that's the only minutes they'll get that week unless you wanna sacrifice anyone else.