I feel she is real sumi coz agar roop badhla hotha her face would be different in her nagin form
Who is mahir ?
I guess mahir was the destined nagraj and he belongs to nagclan but since sumi knew this she exchanged vikrant with mahir and has done some magic to make mahir unaware of his powers which will come out when bela is in danger and mahir is the only person who can save her..this answers lots of question like why sumi wants to kill mahir
Probably vikrant killed mahirs parents or they might have kidnapped them when they got to know the truth of vikrant and sumi..
Kuhu can be a nagin but may be she is adopted kid or something
Yuvi can be a nag aswell or if he is a human may be sumi stole nagmani to save yuvi. I feel they were expecting bela to kill mahir first as he is the one with whom she stays and spends time.
But it went against their plan and bela started killing ppl other than mahir so vik came back and started prrssurizing her to kill mahir
😆