I am sorry to hear of the distress you and your sister are experiencing. Based on your letter, it may be that your sister is experiencing paranoia and/or some form of delusion. You said she thinks that people do not want her to be happy and that people outside of her family do not like her. If there is no factual or reasonable basis to her belief then this seems like paranoia. It is certainly possible that she does have a reason to believe others do not want her to be happy. But since I am only getting a very small portion of the story it is difficult to know if she is in fact paranoid.
As for the idea that people eyes change color, this is a delusional idea. It is not possible for people to change the colors of their eyes (conceivably they could if they wore colored contacts). The fact that she believes this and becomes frightened and angered when she perceives it happening seems to indicate that she needs immediate help.
It’s unfortunate that her in-laws recently asked her to leave the house while she is pregnant. Arguably, she needs their help now more than ever. Presumably they did this because they do not know how to handle her behavior.
I am unfamiliar with how the mental health system works in India. My suggestion is that you do the only thing you can do: continue to take her to therapists or doctors until you find someone who can help her. Is there a hospital that can help? What about some sort of residential living facility or a place that offers help to pregnant women?
I wish I had a better and easier answer for you but all you can do is to keep searching for help, and to keep looking until you find someone willing to assist her.
I wish you and your sister luck. Keep searching for help. Please consider writing back to let me know how you both are doing.