Ok. Here is my attempt. It is not meant to be offensive or hurtful...
Is DG the biological son of AG and DG?
I am not adopted so I can not speak of the emotional trauma and the life long process of understanding why and how, grieving, accepting, wanting, doubting, etc. I think adoption is a beautiful thing and my only close encounter with it is when I found out my father and his high school girlfriend had given their son up for adoption when they were sixteen years old. I had the pleasure of meeting him when I was a teenager. He was an adult when I met him and he loved his adopted parents and they were extremely good to him and he has a wonderful life because of it and that would have only happened if he was with the people who loved and cared for him and were able to provide for him. He is grateful and at peace with it and so am I. But, I am sure growing up he had a lot of questions and doubt and feeling of abandonment and on and on. He was fortunate to work through it and I am sure it is a life-long process.
Some children who are adopted suffer deeply, they never heal, they feel unloved, rejected. I have read profiles of murderers that have been adopted and the link to adoption is a critical identifier to the past and present problems the child or adult encounters. I can research and link this if it is necessary. I am no expert but it could play into part of his motive or built up emotions and pain and suffering. I personally would not see this as an excuse to justify his behaviour or his acts of murder (if he is guilty, of course). It is simply an observation and a question I have raised.
I have not seen photo's of DG's siblings that may show a striking similarity or not in their resemblance of one another. By that I mean, do they look related? Is it obvious or not? The dynamics of the family could be very hard for him to comprehend. If he is the oldest maybe his siblings are the biological, maybe they aren't. Maybe his ADHD eats away at him because his birth parents are responsible for that. It could have a lot to do with his psychological capacity. It could be his desire to be someone else (Matthew Hartley).
What does it have to do with anything? I don't know. I am making an observation/question based on human behaviour and maybe my intuition (for lack of a better way to understand myself why I question this). I wonder if his parents and siblings will ever be able to convince him to do the right thing. If he is adopted and not in a good relationship with his family it could be a great possibility that they will have no impact on him in a positive way. It would be very unfortunate and difficult for his family. I understand that.