My son in law is adopted. He was converted properly by orthodox rabbis in the states. His adopted father is dying. When his father passes on does my son in law observe a normal Shiva, and does he daven before the Amud and say Kaddish for the next 11 months? He seems to think that according to Halacha he is not supposed to. His adopted father is Jewish (reform) and he has no idea who is birth parents were. My son in law is a very frum yid and wants to do what Halacha says about this issue.
It is most appropriate for an adopted child to practice the mourning customs over his late parents. He should "sit Shivah" and say Kaddish and daven from the Amud for the eleven months. (Tshuvot Vehanhagot 3; 374)