In which of the following pair 2nd person doesn’t sit second to right of 1st person? 

We have: B is only daughter of F, who is married to D’s only daughter. Since, F is married to D’s only daughter, that means F must be father of B. D’s gender is opposite to F.G is brother-in-law of D and is unmarried member of the family, that means D must be married to G’s brother.  Let’s say (1) is brother of G and F is married to (2). C and B are unmarried member of the family and are off opposite gender. Based on above given information we have: Again, we have: D sits third to left of B. Since, C is unmarried member of the family, thus C can’s be (1) & (2) at any possible condition. Only two married couples are there in the family. E is the daughter of H, since B is only daughter of F, thus F and H can’s be married. Either both or none of the parent is alive, that means H must be father of E and is married to D. C is an immediate neighbor of C’s father and C’s mother. C and E doesn’t sit together, that means C is not the child of E. If C is the son of F then A should be Mother of C but, Two person sits between C’s father and A from this statement C is also not a son of F, thus only possible condition is C is son of H. Since, gender of C and B are different, thus C must be brother of E. That means we have two possible position of C, in case (1) C sits immediate left of D, in case (2) C sits immediate right of D. Based on above given information we have: Again, we have: Only three person sits between E’s brother and F, that means in case (2) F sits facing C and case (1) is not valid.  Two person sits between C’s father and A.  E’s son and E doesn’t sit together, since only two remaining person are E and G, thus E must be mother of A. Based on above given information we have: Case (1) is not valid as only three person sits between E’s brother and F.