Open Question: if i have a child living with me and he is under my legal guardianship can i get him on my medical insurance?

very confusion, but i had a son when i was 14. i gave him up for adoption to my oldest sister. well he is 16 now and is under my guardianship and living at my house we are currently awaiting from our lawyer to hear what the next step is i was just wondering if anyone knew if i could put him on my health insurance. i have blue cross and blue shield and i live in illinois. and its PPO dont know