Savita is a witch, it bears repeating and she is responsible for this whole horrible mess, but let us examine the situation the children. Sachin, Tej, and Ovi find themselves in, independent of who is to be blamed.
In the last few episodes, Sachu seems to be softening towards Archana or at least exhibits a slight shade of guilt. He has the most reason to dislike Archana. He knew her mothering and was abandoned by the only mother he knew, As I have said before, his hurt has embittered him towards Archana and not knowing the reason behind it, he is angry with her. Excusable. Is it excusable to the extent that he is taking it? To break up the marriage of his parents forever? He sincerely believes Archana is bad news for his father and while lying, forging and cheating can never be the means to an end however noble, he still believes he is in the right.
Teju is figuring it all out pretty fast, the math doesn't add up in her head and she will side with her mother. She too has not known the love of a mother but is a stronger person mentally than Ovi. I liked her "thank you" to Archana and the smile when Sulo wished her. Even her monologue when Purvi wished her is feasible given the circumstances.
Coming to Ovi, is it understandable for Ovi to feel anger? Yes. Hurt? Yes. Disrespect and insolence towards Archana? That is a big no. She is a brat of the first order. She is the same age as Teju but has been mollycoddled a bit too much for her own good. It is perfectly okay for the girls to feel confused, hurt and angry at their mother but they still need to behave with a degree of decorum that is befitting an adult which is sadly lacking in Ovi.
Ovi is no petulant child to be throwing such an unseemly fit every opportunity she gets. She is 20, for God's sake and has not been bereft of all love. As Tej once said, they have not known a mother's love to miss it. They have had plenty of love in their lives, their grandma, grandpa, dad and an older brother; it has not been an unhappy existence. The girls have not been mentally scarred as much as Sachin, they were mere babes when they "lost" their mother to their grandmother's evil scheming and the reason they hate their Aai so is because Savita has created a deep, festering wound in them, she has stirred it and rubbed salt in it every which opportunity she has had.
When a mother leaves or gives up a child, there could be bewilderment, hurt and all that but after 20 years of living without her, the hate should not be a constant raging fire unless her absence has caused them to live a miserable existence, which has not been the case in this instance, They have had time to accept their mother didn't want them, the time for grieff and denial has long been over, acceptance should have set in or at least getting used to the idea of living without a mother. If Savita has indeed taken the place of a mother figure, they have not missed much. They have all moved on, Sachin is a successful (?) lawyer, Ovi a succesful model, and Tej a successful bindaas girl. They seem well-adjusted on that level.
Yet Ovi persists in behaving like someone with arrested development. Tej's reaction of anger, stand offishness, confusion is much more realistic than Ovi's constant shrieking at "wus aurat". If an adult (Ovi is an adult) met their long last mother after many a year, side by side with the anger, there would be a lot of questions and a curiosity to know the truth about this person who left them. We see this in Tej, Sachin is a different matter as his feeling abandoned is justified in my eyes, he did know Archana as a mother and missed her. Ovi's hatred of Archana borders on obsession, an obsession that is akin to the one Savita has. Savita's deep-rooted fear is that her son loves her daughter-in-law more than herself, that is the root cause of her insecurity and that fermenting cesspool of hate for Archana.