A family consists of six members P, Q, R, X, Y and Z. Q is the son of R but R is not mother of Q. P and R are a married couple. Y is the brother of R. X is the daughter of P. Z is the brother of P. How many children does P have ?

Q is the son of R but R is not the mother. So, R is the Father of Q. P is married to R 

So, P is the wife of R and the mother of Q, X is the daughter of P and hence of R and so she is the Sister of Q, Y is the brother of R and Z is the brother of P. 

Clearly, Q is the son of P and X is the daughter of P. So, P has two children.