1. At the temple, he mentions that his mom and Kajal had a plan and it backfired - if he had overheard that, he would have known that they were planning to kill Sheela, why doesn't he mention that?
2.He also asks Sheela that if he supports them, will she believe in his love - to which she answers yes.
3.He gave up his mom a bit too easily.
To put it all together, Rohan overheard him mom and Kajal planning to kill Sheela and so Rohan murdered Kajal, hoping to get married to Sheela, but Sheela backed off after the murder making him suspect that something was wrong (in other words, he figured that Sheela was playing him all along and never really loved him). So, he goes to his mom, confesses the whole thing and still wants to get married to Sheela but he needs to convince Sheela. So they hatch a plan (which Abhi overhears) which would be to plan the whole marriage sequence, after all he has promised to tell her everything about Kajal before the wedding, he clearly denies being the murderer, shifts the blame to his mom, they all come together to plan the "ghost" sequence, Vandana denies being the murderer as well and now both of them are in the clear and Rohan comes off as being the "good" guy and "dumb" Sheela just might agree to get married to him because he was willing to give up his mom to help everyone out.
I think this is where Abhi will come in and clear the whole thing.
I know there are holes in my pov, for instance, Rohan crying when he suspects his mom is the murderer, Vandana slapping Rohan because the book went missing, Rohan not telling his mom about going to get married to Sheela...but we can't really expect a full proof logical situation as well.
The other option is it is an accidental death whereby Abhi might have accidentally switched the bowls (rose petal).
I might be completely wrong though, at this point, I just want them to end it and show some fun, romantic scenes between ViSa and Ravya.