Login and Password for the iTunes accounts, or what? There's no login for the phone but you can set a 4-digit security code. I think you will need separate iTunes accounts if that's what you're asking.
The security code is often set by default as the last four digits of the telephone number. Itunes had some updates that messed up our security codes (3 phones) and that is what ATT told us. We didn't even know we HAD a security code.