Instead of 6 players, you should focus on 3, training is way more efficient with only 3 players. Pick the best 3 in your 6 and focus on them. When one fouls out in one game, switch to 2 position training and make him play in the second position.
Simply based on their salaries, I think you can remove your 20yos from your training routine and focus on your 3 19yos instead. Xue Haizchi should be your priority IMO, but I don't know their skills so it's just based on their salaries and potential