Question

d, the son in law of b,is the brother in law of a who is the brother of c. how is arelated to b

Answer 1

This question has been framed in a confusing way. Let me explain it to you. 

D is the son in law of B, is the brother in law of A. The comma indicates that the sentence is speaking about the same subject, that is D.

So, D is the son in law of B and the brother in law of A. 

If D is the brother in law of A, then it means that D married A's sibling [could be vice versa, but let's not confuse ourselves]

D is also the son in law of B, which means that D married B's child. 

B is the parent of D's wife [as D is the son in law]

It can not be A, as A is 'brother of C'

So, C is D's wife.

If C is D's wife, and B's child, and A is her brother. A is C's sibling, and thus B's child, specifying, B's son.