Okay question about, Possessions?

Your soul is in possession of your body.

When you get "possessed", it doesn't mean that your soul is gone, it means that something else more powerful has come in and taken over. And if something else is more powerful, that in turn has to mean that you have some kind of weakness or lack in faith that allows you to be overpowered.

I would not say that it is EASY, because I'm sure if it were easy then we'd see a whole lot more 360 degree head spins.

I think our souls are safety-pinned somewhere around our ribcage. I also think that invading entities don't get safety-pinned to us, they just float around and stir up some sh*t. (Not literally.)

We inhabit our body. Our spirit and body, really become a soul of sorts. I am unsure of how they are connected, but obviously some people have a gift of seeing auroras and other things about people. I don't think it is easy for another spirit to possess one's body unless you do something that renders oneself open. Since this isn't something seen or recognized regularly, I don't think anyone has a total answer for you except it is possible.

There is an old book called Return To Tomorrow. (Still available on Amazon.com.) The person who had the out of body experience speaks of seeing spirits waiting at bars for people to get drunk or wasted so the other spirits could temporarily possess the body and feel the pleasure of addiction being satisfied through the body again. Other points with that story agree with what patients who have died and been resuscitated have told me, so it gives an insight but not a total answer.

I'll have to disagree with your theory here

other souls dont attach themselves to our bodies, but it's other creatures; Jinns

They take over control off the body, and the original soul is just there, but the body only is being controlled by this "imposter"

The soul is an immaginary object, it is of no matter so therefore it does not exist. It is a belief included in the bible. It is not a physical thing so it cannot be connected by cords as you say...

Possession is usually ruled out by mental disorders.

Is it possible? Yes. Easy? No.

Is it as likely as a case of schizophrenia? No.