I am in a similar situation also. I am a S+C to a U18 representative team coming from five different clubs annd S+C to a representative senior team ranging from fourteen clubs. The main issues are with the u18 team as they were being pulled in every direction and do not have the same skills to look after themselves.
In a high level/”talendted” athlete who plays on multiple teams, they are the one constant amongst everything. I think a often underutilised approach to player welfare is player assertiveness. I spend a lot of time talking to players about being able to say no to training and coaches and managing others expectations of them . This often derives from talking to athletes and prioritising. This is difficult for 12/13 year olds but worth a talk with their parents.
Some of the dialogue often goes like this:
” I am now on the XXXX team and I want to put myself in the best position possible to play well during training and games for them and that means prioritising training sessions” or something along those lines.
Our role as S+C is to prepare the athletes for imposed demands no matter how crap those demands are.
Monday:High Day- Club Training (probably high volume and high intensity, you cant win every battle)
Tuesday:Low Day- Academy Training.Tactical: formations, transitions in attack/defence, free play (tactical can be quite taxing so stick to time limit)
Wednesday: High Day GAME DAY , morning analysis session with academy
Thursday:Low Day- Club Training , Recovery/Regeneration from match. light skill work
Friday: Medium to Low Day, Academy Training : Stimulation session for game next day,limit number of decelerations as quite fatiguing on game day -1.
Saturday:High Day GAME DAY
Educating clubs on training intensities could a option and means you both get the player in better shape come training and games. Having one club training high day and one club training low day should be straightforward compromise but then again nothing is straightforward with coaches!
Just my thoughts. Please feel free to critique