At UK Free ISP each email address uses a POP3 mailbox. A POP3 Mailbox is the address of where your E-mail is stored before you dial up and collect it.
This will correspond to your email address. Your UK Free ISP email address will look something like Dad@ukfreeisp.co.uk. You could also set up a POP3 Mailbox address for each member of the family. How about Mum@ukfreeisp.co.uk?
With UK Free ISP you can have as many mailboxes as you like. You can have one for each member of the family if you like.