I'm finding it impossible to get 5 star training. I have it for all but tactics, defending, attacking and shooting. I even went on GenieScout and there are only managers, Ass Mans and scouts, who refuse to be coaches! Do you need coaches with 5 star or will loads of 4 star coaches do the job?
Count the number of points the coaches have in the training area + Determination, Level of Discipline and Motivating
Tactics 20 + 50 total DDM = 5 star Tactic coach
Defending 20 + Tactics 20 + 47 total DDM = 5 star Defending coach
Attacking 20 + Tactics 20 + 40 DDM = 5 star Attacking coach
Attacking 20 + Technical 20 + 40 DDM = 5 star Shooting coach
I use a free program called FM coach calculator.
More than one coach in one training area won't give you better star-rating in coaching. There is no documentation in-game that having more than one coach does anything at all, except preventing medium workloads. The difference between a 4,5 and 5 star rated coach is microscopic in terms of player development.