Nice to Nice: They already replied, wanna leurn about it?
Check: http://www.afterlife101.com/Spirits_Book.html
Would you like to ask them yourself?
Regarding knowing that they are really spirits, try ask them a question that only you and the spirit with whom you are talking know, if he gives the right answer he's being true, if he fails, he's lying to you, easy.
Another advise is, don't try playing with the spirits.

Only God Can Judge Me
الله فقط يمكنه محاكمتي

I am you and you are me, if you love i love, if you suffer i suffer
أنا أنت, و أنت أنا, إذا أحببت نفسك أحببت نفسي, إذا عانيتَ عانيتُ