Sorry if I am not entirely agree with you. Here is what I feel. Time & again, Toshihi & Raman talked to Ishita about not brining her into their house but Ishita felt sorry for Shagun's plight.
Now that they have got Adi with them, they are only hoping for him to get used to them and attach to them before they take any drastic action against Shagun. Toshiji has never accepted her (Shagun) as an insider, I mean family. She keep taunting her as a guest and also Raman tols her on face that she has no place in his life and she should not behave like she still has some values in his life. This he has told even in front of Adi and he also told her that Ishita will take care of Adi as her own son and will be a good mother for him. So they both are just waiting for Adi to get a hold and mingle with them and accept them as his own and they are very much aware of Ishita's plight but they are helpless with their love for the kid.
Even Ishita knows this and that is the only reason she is trying to make it easy for Adi to get attached to Raman, so that Raman need not have to long for his son. She knows the value of a kid in a parent's life as she felt it with Ruhi. If she could feel so much with the thought of loosing Ruhi with whom Ishita has only emotional bond, she can understand Raman's feelings as Adi is his biological son who was away from him for almost 7 years.