2 icloud acounts

My husband has an iPhone 5s, and my stepdaughter has an iPhone 4 as this is her first phone.

They both have same iTunes and iCloud account. All we want to do is disconnect the iCloud account from the 4s, and switch this off on her phone as when we are deleting some of the contacts that are in the 4s, which are the same in the 5s, it's deleting in both phones, so we do not want to delete the account and clear the 4s in case this happens with the 5s.

We have also deleted the 4s account that was showing on the 5s, so they were not connected but the same thing is still happening. I have also turned of the iCloud backup on the 4s, but still has made no difference. Can you please help?