Trainee A is awesome, great secondaries, good amount of skill points for his age and of course great potential. You should decide what is more important to you: keep him and have an awesome player for season to come, or sell him for a huge sum of money to help the rest of your team. This question doesn't only have to do with what's best for your team, but also what you think is more fun.
If you decide to keep him, you should do a little more outside training in Passing and OD (possibly JR if you like that) and some more JS if you want him to be a proper PF. Depending on your preferences, I'd train both OD and PA to 9-12. After that just train his secondaries according to your preferences (more IS if you want to attack inside, more ID/RB if you want to attack outside and don't need much IS, or more SB/ID if you want to run 2-3 zones against inside attacks).
If you decide to sell him, put a lot more focus on the outside skills because players B and C need a lot of PA, OD, DR, HA and JS.