Your father's father is your grandfather.
He would be the father-in-law.
He would be the father-in-law.
Well to you he would be your cousin To your father it would be his nephew.
Yes, you can call your father's sister your paternal aunt, but few would bother with that distinction. Most would simply call her your aunt.
Because the priest guides you like a father would.
My father's sister would be my aunt, and all of her children would be my cousins.
Uncle
Farfar or morfar, it depends on the side of the family. If it was my mothers father then I would call him morfar but if it was my dads father then I would call him farfar.
Catholics do call God father. Not to do so would be heretical as Jesus, himself, said we should address him as Our Father.
Most would call it "unresolved issues with your father".
She would be your great-grandmother.
He would be your cousin, or your father's nephew.