First of, try to get more coaches. You won't get effective training with only one coach.
The next thing is, that training sessions have the most effect at eight sessions. Every additional session has less effect.
Therefore most people end up with like 10/12 sessions on a single player.
Back to your questions: Splitting up those sessions is not really good, as long as your coach is not an allrounder coaching beast.
Most people tend to go for one coach for a single player early on, so 10 sessions per player.
Also you do not need to train your whole squad. Just train the ones you are using /going to use in the matches.
With facilities capping your staff members, you'll get problems, when training more than your main squad.
As a side note: Training your more than five people is only useful, when you train an upcoming player, that you are going to use soon, or when traning some streamer with a few sessions to raise their revenue.
Your players have to play at least 1 soloQ per day, if they don't play after a day, their ELO will start to decay. I'm almost new too, but maybe I can help you a little with the basics.