7 people in one head sounds like a lot! I don't have anything remotely like you myself, so I can't exactly relate, but I have been to psychologists, and I just wanted to tell you that they only want to help you! It may feel like you're gonna be some kind of curious test subject (just assuming you feel this way), but I promise that they will do what they can to help you, to be a happier and mentally healthier person!
So if you want to practice talking about it, how about some simple questions? Like... what happend when the first one appeared? Was it just out of the blue, or a gradual process? Did perhaps something happen that triggered it (that you're comfortable sharing)?
Just remember though, no matter what's going on with you and your head, it's a big, brave step to go seek help! You deserve all the praise for doing so
and of course, only share what you're comfortable talking about!