You could really benefit from a bit of Googling. Roman naming practice: praenomen (given name), nomen (name of the gens or clan) and cognomen (name of a family line within the gens).
That Justin (Martyr) was known as just Justin says only that he was not a citizen of Rome, nothing more, nothing less.
The Flavian family were Flavians before they became royal. Josephus took their name because he was under their patronage. Nothing strange or out of the ordinary.
You are finding "causation" in "coincidence" and in "correlation." I can hardly wait to find out how the "DaVinci Code" fits in.
Justin was born in
Flavia Neapolis, theoretically he could of being named Flavius Justin
Titus Flavius Justus (Greek: Τίτος Θλάβιος Ίούστος, flourished second half of the 1st century & first half of the 2nd century,
born 76) was an aristocratic, wealthy Roman Jew.
Then another Justus . Justus of Tiberias
Fourished second half of the 1st century & first half of the 2nd century,
born 76)
Flavius Justus - Wikipedia, the free encyclopedia
Justus of Tiberias - Wikipedia, the free encyclopedia
Justin Martyr - Wikipedia, the free encyclopedia
Jesus Justus - Wikipedia, the free encyclopedia
There is another called "Fabius Justus*
The letters of Pliny the Consul with ... - Gai Plini Cecili Segon - Google Books
another called "Justus Calpernius Piso"
Justus Calpernius Calpernius (Piso) (b. - 117) - Genealogy
Then there is some biblical Justus
Joseph called Barsabbas (also known as Justus)
In the Christian New Testament, Joseph Justus (also known as Barsabbas)
---Barsabbas = Son of Saba (Jo-SEBA) (joseph) (josehpus)
Justin - Name of early saints, Latin Iustinus, a derivative of Iustus, from iustus (“just”).
another
Jesus Justus or Iesous ho legomenos Ioustos (in Greek) is referred to by the Apostle Paul of Tarsus in Colossians 4:11
another
Justus is recorded as a member of the group of three Yahudis which included Paul's fellow prisoner Aristarchus, Mark (the cousin of Barnabas) and Justus.
Barabbas - Wikipedia, the free encyclopedia
Barabbas or Jesus Barabbas (son of the father and Jesus, son of the father respectively)
Acts 18:7
And he departed there, and entered into a certain man's house, named Justus, one that worshipped God, whose house joined hard to the synagogue.
3) A Jew, Jesus Justus, mentioned with Mark and Aristarchus by Paul in his letters to the Colossians (Colossians 4:11), is a fellow-worker and one that had been a comfort unto him.
Corinth
... into a certain man's house, named Justus, one that ... necessary to strengthen and fortify
the believer for the ... Paul's efforts in Corinth were not without fruit. .
Ant 20
Justus, the son of Pistus, seized for the Jews, upon the breaking out of the war.
Acts 1:23
And they appointed two, Joseph called Barsabas, who was surnamed Justus, and Matthias.
WTF Justus = Matthias = Joseph = Barsabas = Jesus = Justin = Tiberius = Flavia = Titus
Is this a Typo or Something ????