|A) Brother||B) Sister|
|C) Cousin||D) Cannot be determined|
C is the daughter-in-law of A who is the grandmother of F means C is the mother of F. But F is the son of B.
So. B is C's husband. But C, the lawyer is married to the Doctor So. B is the Doctor. F, the Accountant will be the son of B and C. E is the unmarried Engineer
So. the other mamed couple can be that of grandmother of F i.e, A and D. But D, the Salesman, is married to the Lady Teacher.
So. D, the Salesman, is the grandfather of F. father of B and the husband of A, the Lady Teacher.
Clearly, from the given data, the relation between E and F cannot be determined.