Q: Is it me or does Apple always make this more and more difficult?

I finally was fed up with using one Apple ID to manage about 10 devices (iPhones, iPads, MacBook Pros) across a family of 5 members (3 kids, now teenagers and 20-somethings).  The single Apple ID has been torture...missed phone calls duplicated across devices, sharing of unwanted iMessages, missed FaceTime calls, you name it.  So, an Apple Store employee said, "switch to Family Share...it's easy."

I did this for my two oldest sons.  They run their devices on their own Apple IDs now and I share to them/with them.  The shared calendar is cool.  But, my oldest said, "dad, I want to buy an app with my credit card, not yours, but we're set-up for sharing and it looks like the purchase will push onto your credit card."  "How do I set-up so my iTunes purchases are on my card?"

I'm stumped.  From everything I can tell, Family Share is for families with kids, maybe maximum age is 15 or so because once they get to upper teens, they want independence.  How can I still track them in Find My iPhone (since, as you can imagine with Apple prices, I have a vested interest in the kid and the hardware! ).

It appears Family Sharing is NOT the way to go.

Any body having this problem and if so, have you found a solution for payment independence with a shared member of your circle?