Re: Feeling helpless...
Why did you marry the brother of the guy who did this to your family?
Not being sarcastic but seriously, like are you all related?
I would say if you sister is happily married then Allah mian ka shuakr karo key she didnt marry this other bad person. She would have been crying her whole life and there probably would have been implications to your own marriage seeing her so unhappy.
I say joh hota hai behthar hota hai. No worries.