For training PG and SG, I think that using 5 trainees is best. This allows you to avoid playing each guy in only 1 game, and for the full 48 minutes (which risks guys fouling out and not getting full training, playing poorly due to stamina issues, and so on).
With 5 trainees, there are many ways to set your lineups so that all 5 are very likely to get at least 48 minutes every week (needed for full training). What works best for a given team depends on the stamina and relative skill level of the trainees. One simple example would be as follows:
Game 1: A starts at PG, B backup PG. C starts at SG, D backup SG.
Game 2: B starts at PG, A backup PG. D starts at SG, C backup SG.
Game 3: E starts at PG (set for all 48 minutes). Whichever 2 players are still under 48 minutes split the minutes at SG (this is guaranteed to be one of A/B, and one of C/D).
Of course, this is just one example. I hope that helps :)