What are the reasons raymond Andrews tells amir to give up trying to take sohrab back to america

Raymond Andrews, a man at the American Embassy in Islamabad, says adopting Sohrab is impossible, due to the fact that Amir would need death certificates of his parents (Hassan and Farzana), when most people in Afghanistan hardly had birth certificates. Also, he would need to prove that Sohrab is really his half nephew, which was nearly impossible as well. However, he still gives them the name of an immigration lawyer. He tells Amir to consider adoption.