Concept:
A nuclear family is a small family unit consisting of parents and their unmarried children.
Step 1: Understand nuclear family.
A nuclear family usually includes:
\[
\text{Husband}+\text{Wife}+\text{Unmarried children}
\]
Step 2: Check option (A).
Grandfather is part of extended family, not nuclear family.
Step 3: Check option (B).
Husband, wife and unmarried children form a nuclear family.
Step 4: Check option (C) and (D).
Married children, son-in-law and brother-in-law indicate joint or extended family composition.
Therefore, nuclear family composition is:
\[
\text{Husband, wife, unmarried children}
\]
\[
\therefore \text{Correct Answer is (B)}
\]