How is M related to N ? I. P who has only two kids M & 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 & N.

Data sufficiency questions are designed to check your ability to analyse & categorise information based on underlying concepts rather than calculations. So you should try to observe -  analyse and to find linkages between various statements rather soing lengthy calculations.