well, I'm not too negative on the prospect of you training both of them at the same time. Both need OD and Passing above all else, so training these two skills for most of next season seems exactly right. You're not going to mess up anyone with that. After that, you have to consider what to do - and by then, I'd make B the main focus of the training, while still giving A all the training he can get. A will already be very good by then, so it will be almost impossible to mess him up - it's more about finishing touches than the basics for him.