Who actually responsible for janki's death?

i dont think it's any of the above!

Sharmishta has been shown as way to good to try any of those kinds of things. She would never swap or do anything I feel. She's super positive.

As for the storyline, I'm so confused. I feel like Sharmishta's marriage broke down and she returned home. Shekhar saw her/ she saw him, both of them liked each other and decided to be with each other. That's when Swara was concieved. But then Shekhar was probably already engaged to Janki. Shekhar's parents were obviously not happy about Sumi-Shekhar and the moms conspired to break them up. Probably some misunderstanding happened with Swara where Shekhar believed Sumi cheated on him with her husband or whatever and Shekhar refused to acknowledge Sumi/ her love and left her and got married to Janki (hence the betrayal Sumi mentioned). But then he could never really love Janki the way he loved Sumi (despite having Ragini with her) and Janki probably heard Sumi-Shekhar talk about their love and then fell down the stairs in shock.

I don't know. It's an interesting show and I can't wait to see what happens next!