Visitors visa for mentally challenged sister-in-law

[dchandra]

I want to apply visiting visa for my parents-in-laws and to my sister-n-law who is mentally challenged( she stays at home and she is not having any school education). My father-in-law is a retired government employee. My mom-in-law and sister-in-law are dependent on my father-in-law. I am in U.S from 2007 and hold Green Card from 2014. I want them to come and visit me for sometime. When I was on H1, I sponsored visa for my mother-in-law and sister-in-law and that got rejected,Again I applied only for my mother-in-law within a month though unfortunately it got rejected.
So now after waiting for more than 3 years,I am planning to apply visa for my in-laws.
I heard that if my sister goes along with parents for visting visa there are more chances that even my parents visa might get rejected. Is that true? Is that better to go my parents first and then my father-in-law/mother-in-law can accompany for my sister-in-law visa?
Please help me with the suggestions.

[pb2au]

First of all, it is unlikely that the U.S. State Dept will discriminate on the basis of anyone's mental condition for purposes of a visitor visa. Every individual case is evaluated on its own merit. Your sister-in-law accompanying your parents-in-law will not affect anyone's prospects one way or the other. There are instances where some members of a family have been granted the visa and others rejected when they went in together for the interview. It just depends on the specific case and there is no general answer to this question.