I will blame Ishwari first. She can misunderstand her own son and accuse him but she will never understand Radharani's intentions and never accuse her though her brother warns her again and again about Radharani. She is the root cause of all evils. She could have shut Radharani's mouth instead of keeping quiet and encouraging her. I will be happy if her family is completely destroyed only due to her. Everyone in that family deserves destruction.
Next is Bejoy. He is the worst person who does not think twice before jumping on others and harming his own daughter's happiness in that process. Too interfering just like Ishwari. He will never support Dev independently though Dev bends over to ask for forgiveness umpteen times. Bejoy is too selfish who lacks foresight.
5 crores is a big amount and Dev should not have invested knowing how his family treats Sona's family. Of course it is is his own money but his mother thinks otherwise.
Mamaji is useless. though he is watching the destruction by his wife and son, he wont take drastic measures like taking a firm stand and firm decisions.