I'm gonna answer this, but next time use search, please.
Train only bench and reserve for bonuses, never the main squad. If you don't have enough players on the bench+reserve, buy some old cheap guys.
You only need 8 players to cover all the bonuses. Just remember:
M*, AM* and ST count as attackers
GK, D* and DM* count as defenders
DM*, M*, AM* count as midfielders
Train for bonuses using only Very easy drills (Warm-up, Skill Drill, Video Analysis). Add 2 of each for a start and see, how it goes. Try to combine drills in a different ways to find the perfect recipe. I'm not telling you the perfect combination because it depends on what players you have in the training schedule.
It is possible to spend only 13-15% of Condition loss with 2x videos or twice of that amount without videos to climb from 8% to 10%. However, as you probably know, there's a daily limit of videos you can watch (when farming green packs or doing bonus training), so I don't recommend you to waste it on bonus training since you do it with bench+reserve guys. Their condition is not important. Farm greenies instead.
Good luck with training!