Hey.. The thought had crossed my mind too.. If any of you have followed 4 Lions previous shows, that's one thing that has been constant apart from the love-hate lovestories.. The hero's family is somehow responsible for the heroine's tragic past, or has something to do with her family..
When they first showed Ishaana as a con-woman, I was reminded of Anika's nightmare where she got separated from her sister. It's quite possible that she was found and adopted by the 'Pappa' who raised her, and she's actually Anika's sister.
Also, the theory about Anika and her family being originally rich, and the Oberoi senior brothers being responsible for the bankruptcy and elimination also seems plausible. That would in turn link the two families, and Shivay-Omkara's girls and prove Dadi's prophecies regarding their soulmates right.
But yes, one thing I can say for certain is that, Gul has always kept some skeletons in the closet (about the female lead's family and the male lead's past), which get revealed just when the hero-heroine are on the right track, adding chaos to the already mushkil prem kahani..
I'm not so sure about Soumya being the 3rd sister, coz by the looks of it Anika had only sister (Chutki).