Welcome to AF!
You could create a shared gmail account for them and link it to both tabs? If you add your debit card details, there's an option to protect paid purchases with a PIN so you could still control what apps they install if you were the only one who knew the PIN. As far as I'm aware, you can tie the same gmail account to 5 (maybe more) devices and apps are tied to an account, not a device so that would also solve the buying apps twice thing too.
That way, if you sent the mail account calendar invites, they would appear on both tabs.