But who does a regular JW sees as a brother or sister to Jesus?
They see whoever the Watchtower tells them to see.
Ironically, Christs brothers really do include the 144,000 because they are from the literal tribes of Israel. Jesus was, and is an Israeli. They are all brothers.
These are Christs brothers who will be evangelizing the world during the Great Tribulation. Church Age believers (Christians) will be long gone by then in the Rapture.
During this time God prepares the nation of Israel and the world for the 2nd coming of Christ who will defeat the Anti-Christ and save the world from all of his various wars that he has started.
Once seated on his throne in Jerusalem, (after Armageddon) the nations (people that are left) will be gathered before him and the sheep and goats judgment will then take place. Those that were friendly toward the Israelis during the GT will be allowed to enter.
Those that were aligned with the Anti-Christ and blamed the Israelis for everything will not be allowed the enter the Millennium.
A cursed and disfellowshipped Jewish King who walked out of a tomb 2000 years ago will then rule the world with fairness and peace for a thousand years.