My nephew just passed away. His biological father converted before he married my sister but after my nephew was born with an illness he divorced her and went back living like a goy. Neither he nor my sister are still living.
Since we do not know what his father’s name was when he converted, do we name my deseased nephew ben Avraham Avinu or after his adoptive fathers hebrew name?
Yo can call him ben Avrohom, as the standard name for a ger is Avrohom.