The original sect was not Jewish. It was Adam whom we all descend from. Adam was given the 7th day sabbath. Abraham also wasn’t Jewish. Isaac wasn’t Jewish. Jacob or Israel was the father of the 12 tribes. Moses was of the tribe of Levi. From the tribe of Judah came most not all of the Jews including King David and Jesus Christ (Yehoshua HaMashiach).

To answer the question of the original Jews, you probably will want to look into the differences between Mosaic Jews vs Hellenic Jews. The distinction became more stark around the time Jesus came to earth. They started splitting into various factions, Pharisees, Saducees, and the Essenes.

Many are coming to understand that the modern descendants of Israel make up the original people of England, Ireland, Scotland, America, Canada, Australia, as well as some European peoples.

You can find out more from Yair Davidy who did an extensive study on this. His website is

https://britam.org/