Hi,
I think im going nuts but it just struck my mind as to why Nishikant wanted Bani to take the girls to Jai after his death.
We know that Kiran Singhania came from a business family and Jai'a dad and Kiran's dad were friends and business rivals. After Kiran's marriage to Nishikant, Singhania family could have disowned their daughter for marrying a commoner and she being the only child (that is Kiran) made Jai the trustee of the entire property until Bani reached a certain age. Maybe the two crystals that were shown at the beginning of the serial an indication or a reminder to one another about this legacy.
Now coming back to Park Road, Singhanias may have owned major property or their palatial house would be there and the mere mention of this brought back memories and reminders of the past. And this Karan character may have been a common friend or someone Jai, Roshni and Kiran knew or could Karan be Bani's biological father?????