Multiple cookies on the same computer

Hi all. Newbie here. I have set up a blog site where my family creates posts and they get emailed to members of the family. To keep up with their identities, I created a script for each family member to run (dad.php, mom.php, etc.), and it sets a cookie on each computer and uses sessions so I know who is connecting. It works great unless I want to share a computer between two users. I thought I had a solution: install both Firefox and IE on the same computer and set two different cookies. But this doesn't seem to work. My question is: Is it possible to set one cookie for IE and another for Firefox so that, depending on which browser is used, I can tell who is connecting to the blog? If this is not possible, is there another easy way to do it? Thanks for your help. - Ken Watkins