So black magic is out, as Tai admits giving Lata weird drugs.
And that doll, I believe is remotely controlled by someone who has put cameras in it to record everything that is happening as evidence.
That someone could be anyone:
1.Kishore who never died (most likely him, because without hard core evidence noone will ever believe him if he accuses Tai of any wrong doing)
2.Pyaare to blackmail Tai
3.Kartik who may now wants to know the truth
Aniket may not be negative but there are chances he will because, he said he doesn't care what mum does to anybody else in the house, he just does not want to loose Survi. In other words he is fine with his mother doing evil to Lata and Kartik and others. This makes Aniket half evil.
Aniket will become full evil when either Kartik marries Survi or when he finds out that Survi loves Kartik not him.