P and Q are married couple. A and B are brothers. A is brother of P. How is B related to Q?

Brother in law  

↑ or ↓ ⇒ Upward or downward line shown "generation gap" .

   =    ⇒ Double lines shown "relation b/w Husband & Wife"

   —   ⇒ single line shown "relation between them other than Husband & Wife".

‘+’ means Men’s category

‘–’ means Women’s category

P and Q are couple but gender of any is not clear but A and B are brothers that is sure both are male.

So, relation is Q to B is Brother in law.