Forgotten ITunes Account Details

Where someone has three Itunes accounts (one for iphone, one for ipad & one for ipod) and only one off the email addresses is now valid how do you merge the three accounts together. No icloud back up has been done on the iphone so we want to ensure when we do anything that contacts and content on the iphone aren't lost. Unfortunately it is the itunes account associated to the phone that the email address is no longer valid for and they cannot remember the password for that itunes account either.