My two PlayStation 3 controllers log in to the same profile - why is this happening and how do I fix it?

My sister and cousin are looking forward to playing Minecraft on our PlayStation 3.
They called me to help, after they couldn’t get both of them into the game. Apparently, both the controllers are logged in to the same profile, and both controls are able to control what’s going on on the screen (like navigating the main menu).

Even when I used the second controller to log in to my own profile, it decided to log both controllers in to my profile, instead of keeping controller 1 on hers, and controller 2 on mine.

Can someone explain why that is happening, and how I can make it so both are on different profiles?