Welcome to the Apple Community.
Your problems arose because you used the same account for two people, each should have their own account, if one person is underage you can set up an account in your name and let him use it, don't just let him use your account.
More details about your back up issues may help someone to assist you.
You are correct in that each should have his own account. But because my son is under 18, he cannot have his own account. I would still be in charge of it and monitor it. I was not going to lie and falsify his birthday. So, Apple would not let me create a separate account for the App Store or iTunes for him.
I am also having issues with iCloud and iTunes and synching my PC with the iPhone. What a PITA!
The words "user friendly" are not in Apple's vocabulary!
This will be the last time I ever buy and Apple product!