To set it up as POP you need to delete the account, reboot the phone by holding the HOME and SLEEP buttons at the same time until an Apple logo appears (about 10 seconds), then add it back following these instructions: Forcing creation of a POP or IMAP email account
I understand that you have used the same account for many years, but the technology is also changing constantly. Years ago the standard was POP (Post Office Protocol), which was designed at a time when it was inconceivable that anyone would access their email from more than one device. When people started using multiple devices, for the most part they wanted to see changes on one device mirrored on another. A new standard, IMAP (Internet Mail Access Protocol) was developed. With iMAP the master copy of all messages resides on a server, and multiple devices are kept in sync with the server. So if you delete a message from one device it is removed from the server, and then removed from all other devices when they next sync. This is the same way Microsoft Exchange works. Other benefits of IMAP include the ability to have multiple mail folders that are kept in sync across devices. In your case you could use this to create a separate folder for each family member, so they could move messages to their own folder and not clutter up the shared Inbox. Most computer mail readers can even automatically sort incoming mail into folders based on the contents of the message.
IMAP is considered a "higher level" standard than POP. When you create a mail account iOS devices query the server and ask what it supports; if it says it supports IMAP then the account is automatically configured for IMAP. So if you really want POP you must fool it, as described in the link above. In my experience Android devices default to the highest level protocol also, and I suspect newer Blackberries do (although it has been 15 years since I used a BB).
