I think bandini is just corrected and edited version of kasam se. with a bit different culture, new environment and new actor + character
KS(kasam se) had the same plot gal ran away (pia) at her wedding day, here guy does it and sister get stuck with groom. here they made excuse kundali and bride stuck with DM
like ks family and hubby does not accept marriage then slowly with her behaviour they turn towards her
same happen with santoo
guys sis always hate her sis in law : compare jigyas and moti ban
bani in ks ask divorce to save her hubby 's ijjat and prop here santu does it
bani's youngest sis ran with her nephew in ks here also sis ran with hiten
so old wine in the new bottle
let's see how they unfold the story