How do you disown your father?

Your father's father is your grand father and your grandfather's father is your great grandfather.

Then you don't have a father

Can't happen unless there's some step-relationship here, such as a man marrying his step-mother, the wife of his father. That still makes you your father's son in any case, but now you have become...

Absolutely!

Whether "your father and I" or "your father and me" is the correct construction depends entirely on how it is used in the sentence. "Your father and I" would be correct only where the use of "I"...