That's why I think he's in on it. 😉
Rachna has a history of telling other's the what's what: Daadi and Daasi about the spilt oil, Sarla about Pragya's odd behaviour, etc...
And given that Purab clearly doesn't know the truth -- Akaash is the only other person who could have gotten Abhi to sign the property papers over to Pragya. Yes, Abhi also trusts Daadi (who I believe is also in on it also - I mean, she was at some hospital while Pragya was in surgery) but that would seem suspicious, no? Why would Daadi hand Abhi anything to sign. He would have found it odd - even in Devdas mode.
I also think RoDaadi is in on it, because of a comment she made once to Sarla and Bulbul when she found out that they had hid Pragya's pregnancy from her: One day I'll find something out, and I'll keep it myself -- then you'll all see how that feels.
So I'm pretty confidant that: Daadi, Akaash and RoDaadi know the truth. The only person I still haven't pegged is Bulbul. I kind of want her to move into Mehra Mansion, so that my suspicions can be confirmed. She could help Pragya torture Team Evil. I mean, she already joked once that Abhi should give MM to Purab as a gift, so she could operate off of that. It wouldn't be so much of a stretch. I say she move in and claim Aaliya's room as her own -- just because Aalu's reaction would be priceless and I'd love to see that 😆 And since Robin told Pragya that Abhigya's room shares the same water supply as Aaliya's then Pragya wouldn't have to turn it off to inconvenience herself.