Raj's parents are Harjeet and Amrit Bajwa. Mohini is his stepmother.
Preet's mother is Amba. Her father, Charan Pawania, died before she was born.
Pawanias and Bajwas have been enemies since before the beginning of the show.
Amba's mother in law hated Harjeet's father because she believed that he killed her husband. Harjeet always hated the Pawanias but he hated them more after Amba's brother in law, Jagan, tricked Harjeet's sister, Swaroop, into sleeping with him and then dumped her. Amba started to hate Bajwas after they killed her husband although it is unclear whether this is true; it is implied that Jagan himself arranged for Charan's murder.
The hatred between the two families reached breaking point when Harjeet's eldest son, Raman, and Amba's eldest daughter, Simran, started an affair. Simran got pregnant and Raman was forced by his father to get engaged to another girl. Just before the leap, the pair eloped and Preet allegedly killed Raman with a shot to the heart to which Harjeet responded to by shooting Simran. Of course, this made the two families hate each other even more and led to the break up of the Bajwa family; Harjeet married his mistress, Mohini, whereas Amrit left the house with Raj.