I just started watching this show but from what I watch so far I wouldn't place the blame on either Lajjo, Nikhil, or Ishana. Rather no one can really be blamed for the situation at present. Nikhil did a huge, HUGE favor for rescuing and marrying Lajjo at the cost of his relationship with Ishana. He helped out Lajjo without thinking of where to go or what to do. All he thought about was in trying to help and he did. All the events that happened thereafter, some were in his control some were not. He could have better approached the situation as to where he could put/keep Lajjo until he could talk to his parents about his decision of marrying her (but being honest nothing would have made the situation any different) and the situation she was in. Or after realizing how his family is reacting, he could have probably help Lajjo in her education or something. Lajjo is just as an innocent party within the whole situation.
However, Ishana's decision in cutting herself to kill herself is in NO way Nikhil's fault. She was the one he consciously decided that she didn't want to live due to her losing Nikhil. In no way do a person have a right to blame another for themselves commiting suicide. It is just plain selfish to place the blame on someone else when the problem begins with yourself. Plus Ishana kept on pushing Nikhil away trying to move on but she flipped when she heard Lajjo and Nikhil laughing and talking on the phone and he didn't come to meet her for their anniversary thing. She made the move and she is the reason as to why her mother is hurting and is now reluctant to leaver her alone. Her mother is hurting because Ishana carelessly threw her life away for a man without thinking about the others, about her mother that she would be leaving behind.
Barkha is another can of worms that I just don't want to deal with. For the longest of continuously holding homage to your deceased son is one thing but to continuously hold blame over your other son (who might be or might not be responsible for his death) for his death and to use your love and affection (something that Nikhil desperately wants) as a bargaining piece is just downright psychotic. However, I can understand where you might react one day when your son just brings in a random stranger and claims that this is your wife and here. Any average mother would go complete bonkers and wouldn't accept it. However, after a reasonable time frame they would try to understand the situation that their child decided to make a decision and try to go on from there. But Barkha is not doing that, she is not interested in doing that. In foremost she wants Lajjo out and only interacts with Nikhil to either emotionally blackmail him in throwing Lajjo out.