Q: How to keep sharing but remove payment option?

Ok... Created sharing, created parental control, so payment method is also ''shared''...

But now, as my kid started a program at school with BYOD, he needs full access to his iPad.

How can I:

1) give him control so he can install free things required at school without waiting for my approval,

2) keep family sharing (so he can still access my purchases - music, selected apps, and so on), but:

3) without leaving my payment method (credit card) so he could do purchases I would not authorize (with or without intent) ?

Thanks,