Madan's brother's uncle is Karan's father's brother. What can be the relationship between Madan and Karan?

Two persons are going. One is the father of the son of the other. What is the relationship between the two?

If A is the father of B, C is the mother of D, B is the brother of C, and E is the son of D, then how is A related to E?

If A is the father of B, C is the mother of D, B is the brother of D, and E is the son of A, then how is E related to C?

If A is the sister of B, B is the brother of C, and C is the father of D, then how is A related to D?

If A is the brother of B, B is the sister of C, C is the daughter of D, and D is the father of E, then how is A related to E?