Arpita's parents seem very rich and maybe Arpita is their only child so before they could bequeath anything to her, she died. Sr Scindia may be thinking that if he milks Arpita's parents' emotions and somehow makes them believe Aarti is Arpita part 2, he is steering them toward bequeathing everything to Aarti.
In fact, this may be the reason he agreed to Aarti as the new bahu - he may have believed that a widowed mother of a child will be very submissive and go along with all his grander plans.