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.

R is the husband of P and Z is the brother of P. So, Z is the brother-in-law of R.