The Rane side of the family doesn't know that Malhar has decided to not have any intimate relationship with Kalyani until she has completed her studies and found a job,so they may believe that she is pregnant by him and he not correct them.
The others also may believe it,since recently Kalyani told Anu and AS something from which both women guessed that love has blossomed between the two.
The timing is another issue,but I doubt the entire family will worry about that.
Malhar will obviously be perplexed and demand answers and,upon being told that the baby is Rachit's,I doubt he'll believe her TBH,since he himself made sure that he couldn't come near her and then Kalyani later admitted she wasn't with him out of her own free will but due to him and Sampada blackmailing her using Pillus health issues and that since then she hates Rachit.
Eventually Kalyani will have to tell him the truth.