If a boy was born to a Jewish father and non-jewish mother (thus the child is a goy) and on his 8th day he receives a halachically acceptable brit milah and then later on he becomes a geir later in life does he have to re-do the brit milah. What if he doesnt know if the brit milah done on him was leshaim shmayim by his parents? If he becomes a geir does he become his hebrew name ben avraham or does he become his hebrew name ben his jewish fathers hebrew name. If he is geir does he say kaddish for his biological jewish father? Does he say kaddish for his biological jewish mother who also becomes a geir?
Being that the circumcision was not done for the sake of conversion, the milah needs to be “redone” i.e. blood drawn for the intent of milah. He may use his biological father’s name to be called to the Torah. He may also say kaddish for his biological father and convert mother, although he would not be required to as by standard Jewish parents.
See Rambam, Milah 3:7, the Tzafnas Paneach there interprets the Rambam to be of the opinion that if a milah was given to a non Jew for the sake of performing the mitzvah of milah, this would suffice if at a later time he decided to convert. See also Meiri, Shabbos 135a who implies so as well. This is the opinion of Har Tzvi Y:D 219.
Many interpret the Rambam differently and disqualify such a milah. This seems to be the opinion of the Ramban in MIlchamos Hashem to Shabbos 133a. See Igros Moshe Y:D 1:158,318, Maharam Shick O:C 144. This was also the opinion of Rav Elyashiv.
With regards to the name and kaddish he may choose to consider his biological parents as parents, however on a kesubah or other legal document, see Igros Moshe 4:26 that the father should be referred to as “the one who raised him”.