i wanted to make a post about niranjan but since you made it so will be expressing my POV here
reasons why Niranjan is negative (according to me):
(1) entry of niranjan scene... the pooja scene... due to his physical appearance and the background music my first thought was *okay so he seems the negative character of the show* also his actions and words are very mysterious and have double meaning at times
(2)his behaviuor towards his elder son... He did not even let shlok hug his brother properley
(3)he is extra sweet with the people he thinks can benefit him... example is of astha dad
(4) it is shown that he loves shlok too much... But if he loves him the most then why is he living with anjali whos is responsible for shloks condition and he is not even angry, even a bit, on her
(5)Anjali on the other hand it a very obidient wife and she wont do anything without niranjan's permission so as far as my thoughts are concerned I think whatever happened in the past niranjan is pretty much involved in the tragedy and and the blame might have been thrown on anjali because she seems like a puppet nad can never disobey niranjan
(6) in one of the flashback it was shown that shlok is leaving the house and niranjan is trying to stop him...niranjan did not seemed disheartened with the tragedy much... If he would have loved him soo much then he would have given some punishment to anjali for ruining the life of his beloved son
(7) he asked shlok to go back to mumbai... because maybe his reputation is much more important to him
(8) he allowed him to stay and granted the permission to handle the situation in his own way... he is very much sure that shlok will do something to take the revenge OR will play some tricks OR chalk out some plan ... ofcourse niranjan is not nave at all
(9) in the car shlok says that aastha is responsible for everything and he was furious on her and niranjan heard that and did not said anything which show that he agreed with him and in the last episode he said to aasthas father that it is nothing to worry about and that it not her fault etc. which contradicts clearly...
Well, there are many other scenes and which proves that niranjan is negative...