2 positions training give less than 1 position training, but it allows you to train 3 more players per week ; for exemple Pressure for PG/SG give around 60/70% of Pressure for PG.
Some trainings like Jump shot, 1on1 and rebounding are not available on a single position, it is always 2 positions (or for the complete team, but i would not recommend it).
So it kinda depends on how many players you are training. If you are training 3/4 players, always train on a single position. If you are training 5/6 players, it depends on multiple parameters.
For guards, I saw that many people are used to train 6 players with 1on1 and JS for few seasons, than they sale 3 of them and focus on the 1 pos. training like Pressure and Passing
Usually, you want each player having 48min per week on the trained position.
I also recommend you to get a level 4 trainer (at least) if it's not done yet.
I hope i did not confused you.