See if you see both doesn't have direct relation with Saransh. She is Masi and he is Chachu but both loves him equally just like real parents.
Also, if Rudra can bring Preesha with Saransh home even after MU and tells Ballu that they can't be parted so that means he knows how important Saransh is for her.
So do you think he will separate PreeAnsh after knowing the truth? No, obviously not, never.