A son will never doubt his mother. I have a feeling that Arjun remembers his mother. You can see that look in his eyes. According to the picture of his Mom and by the sound of her voice in 2days episode, she seemed quite harmless. How can she be a terrorist. Somebody has definitely framed her to cover his tracks.
Nobody knows who is Arjun's real Dad, so till now we cannot say if he is an Ahluwalia or Singhania. Amrit and Sudhir know much more and they said they will keep it a secret for the sake of Arjun and Arohi.
I think that Amrit is also keeping a secret and Sudhir is not aware of the same. Is Arohi an Ahluwalia or a Singhania?, because she was friendly with RPS, which is evident from the photograph of Amrit kept by RPS.
I do not think that KSA is aware that Arjun is not a Singhania. I do not even think that KSA is aware that Arjun is an orphan.
Very confusing.