NO, they were NOT the very first Christians. The first Christians were Jewish believers and others who lived around him. Some were romans, too, but they weren't roman catholic. They were believers in Yeshua and Messiah.
DUH, EVERYONE knows that Jesus, Mary and the apostles were Jewish. It is they who started what became the Catholic church. For hundreds of years all KNOWN christians were Catholics and the church eventually became known as the ROMAN Catholic church. Until Martin Luther came along.....