How to change apple account in the ipad many times?(can't sign out)

Question

How to change accounts!
I have multiple accounts not me but the whole family has apple accounts since we all are apples. Anyway everyone has a no credit card account except my dad. His account is synced in my sisters iPad. My dad changed the password so that we don't buy stuff the problem is we can't sign out of our dads account! I mean when we go to ipad:setting->store we already see that its already signed in my sisters account! But the problem is whenever my sister wants to update or download a free app it gives my dads email & wants us to fill the password! We already signed out!
We tried logging in via itunes store then syncing the ipad but nothing happened!
The apple retail store said after you submit the email of your ipad the only solution is to format it. But here is the big problem lets say we formatted it & after few days/months etc we wanted to buy an app we couldn't change the account to our dads account! Since we already are having trouble logging out of our dads account.
So please tell me how to change the account many times! Because I couldn't change it in the iPad nor in iTunes in my iMAC.

Answer 1

The apple retail store said after you submit the email of your ipad the only solution is to format it
Your iPad does not have an email address.
You will need to add a CC card to verify your account. The CC info can then be removed and the account used normally.
It would likely be easier to simply update the apps on the computer then sync the iPad.
iTunes can be authorized for all accounts then all apps can be updated at once.