Anjali you have rightly pointed out hereditary vs. upbringing has always been a debatable topic. All aspects of anyone's life - their character, sense of responsibility, good and bad habits, ability to cope with difficulties, and the faithfulness - are shaped primarily during childhood. The bright memories of childhood can strengthen and warm them during trying times, and, contrarily, those who have not had a happy childhood can in no way remake it. Even if they are not with their real parents their characteristics are always developed. In this case both Sia and Astha have always had parental affection but I think they both in different ways were showered with too much warmth and brought up in very secure environments, and this can play a vital role on how they perceive things now. They were brought up in a lovingly environment but the parental genes are still there and characteristics will surface in them as we get to know them more.
There are some common characteristics between Sia and Astha. They are stubborn in their own rights and fearless. They are ready to fight for a good cause and deliver justice to the wronged. They are also hasty and jump quickly without thinking about the consequences, which is a trait that is related to their father. His idea to run away from everyone without consulting is also seen in his kids where they do not think its always necessary to ask their family before taking decisions.
Sia – Sia has been shown as strong, self-motivated and strong-minded just like Simran. She is also very caring and is concerned for the society more than herself. Unlike her mother Archana who had not thought once about it when kidnapping that how this would affect the kidnapped kids parents. Instead of adopting she ruined a family's happiness. On the adverse Sia after her good friends were dead still thought about them and came all the way to India to look for answers. Regarding her reaction to the reality of her parenthood she took it the same way as we had expected her to. She like another other in her situation would have wanted to know about her real parents. I think Archana providing a false story like money was not something that a level minded person like Sia could easily buy. And if it was indeed money then Sia wants to be there to help them fulfill their quest by helping them.
Astha – Astha not able to successfully pass the medical exams show that this has nothing to do with the upbringing but in fact that sometimes you need the parent's genes as her parents were not doctors. All in her family starting from Simran to Shaguna to Abhi's parents had spoiled her. She has got away with what she wanted and that she believed was because she was a part of them. It is not easy when you are loved so much to be told that you are really no the part of it, So it was why she reacted the way she did feeling lost and unsure. Its not that she did not love Simran anymore or forgot all that Simran has done for her over the years but its that she did not even have a hint that she was not a part of them that made her react this way.