Nanu Purshottam Diwan, being the man of principles that he was, I don't think he would have chosen any selfish woman like Sheila from Dholpur, for his one and only son.
If he chose such a gem of a person Harish, for Avantika. I'm sure that he would also want the best for Anuj.
As mentioned above by my namesake Sonia, I guess PD was fouled in accepting Sheila as his daughter in law. The same way about what happened in the case of Rubel and Payal.
Karma it is.
Sheila might have played a lot of fouls along with her brother to get into the Diwan family, as a matter of fact, all her fouls are returning to her in the form of Rubel. Poor Rubel went through so much before finding the love of his life.