Explanation:

Q, the Doctor, is the father of T. S, the Housewife, is the grandmother of T and hence the mother of Q.

Since there are only two married couples one being that of Q, the grandfather of R i.e.,

U must be married to S. Thus, R and T will be both children of Q and these must be the students.

So, P, who remains, shall be the wife of Q and she alone can be the nurse.

Thus, U must be the contractor and grandfather of R.

Hence, option 4 is the correct answer.