Ok, you need OD, it´s a very important skill! Then you need Passing, Handling and Driving (which all depend on each other). I would do some weeks on OD and later on some switching between different trainings.
Right now it seems, that you have 2 (very) good traninees (Huffmann/Hubbart) and 3 decent (Jaanson/Jellen/Lacasa). I would sell some other player and buy another trainee, so you can do PG/SG training on the skills above. You also could train only 3 trainees, but in my opinion its more fun to have 6 players trained then only 3.
Your choice ;-)