Baptismal names: When they returned to Judaism, they kept the baptismal name, changing their first name to a biblical one.; e.g. Diego Nunes Ribiero became Samuel Nunes Ribiero. Note: Brothers with different baptismal surnames were not uncommon, but upon conversion they adopted one family surname: e.g. Gabriel da Costa from Portugal became Uriel da Costa in Amsterdam; his brother Miguel Esteves de Pina settled in Hamburg as Mordechai Da Costa, and Joao Perez de Cunha arrived in Stuyvesant's New Amsterdam, in 1655 as Joseph de Costa. Some recalled their ancestral home in Spain or Portugal by prefacing it with "De" from; e.g. De Leon.
Until the middle of the 19th century, the oldest son was named for the paternal grandfather: oldest daughter for paternal grandmother; the next pair for the maternal grandparents; and the younger siblings for other relatives -- all whether alive or deceased. Look for repeated name patterns.
Rabbi Malcolm H. Stern (1916-1994), Dean of American-Jewish Genealogy