Question : How is M related to N?

Statements :
I. P, who has only two kids, M and N, is the mother-in-law of Q, who is sister-in-law of N.
II. R, the sister-in-law of M, is the daughter-in-law of S, who has only two kids, M and N.

Explanation:-

From I, we conclude that P is the mother of M and N, while Q is the daughter-in-law of P and sister-in-law of N. Thus, Q is M's wife and hence, M is N's brother.
From II, we conclude that M and N are the children of S. Also, R is the daughter-in-law of S and sister-in-law of M. So, R is N's wife and thus, N is M's brother. Hence, M is either brother or sister of N.