According to Epiphanius in his
Panarion, the first disciples moved to the area of Bashan, which included Pella and Cocabe. Epiphanius claimed that Ebion himself was connected to Cocabe. This is from where the heretical sects the Nazoraeans and the Ebionites arose, according to Epiphanius.
First, the Nazoraens:
Part 29. Epiphanius Against the Nazoraeans
6:7 Thus Christ's holy disciples too called themselves 'disciples of Jesus' then, as indeed they were. But when others called them Nazoraeans they did not reject it, being aware of the intent of those who were calling them that. They were calling them Nazoraeans because of Christ, since our Lord Jesus was called 'the Nazoraean' himself—as the Gospels and the Acts of the Apostles say...
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7:4 They are perfectly versed in the Hebrew language, for the entire Law, the prophets, and the so-called Writings—I mean the poetic books, Kings, Chronicles, Esther and all the rest—are read in Hebrew among them, as of course they are among the Jews.
7:5 They are different from Jews, and different from Christians, only in the following ways. They disagree with Jews because of their belief in Christ; but they are not in accord with Christians because they are still fettered by the Law—circumcision, the Sabbath, and the rest
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7:7 This sect of Nazoraeans is to be found in Beroea near Coelesyria, in the Decapolis near Pella, and in Bashanitis at the place called Cocabe38—Khokhabe in Hebrew.
7:8 For that was its place of origin, since all the disciples had settled in Pella after their remove from Jerusalem—Christ having told them to abandon Jerusalem and withdraw from it39 because of the siege it was about to undergo. And they settled in Peraea for this reason and, as I said, lived their lives there. It was from this that the Nazoraean sect had its origin.
So the disciples, who were called "Nazoraeans", moved to the Pella area before the Jewish war, and that's where the Jewish Christian sects -- whom believed that Jesus was born from Mary and Joseph -- arose according to Epiphanius. To me, that's strong circumstantial evidence that the first Christians believed in a Jesus who was just a man, assuming Epiphanius is reliable on that information.
Epiphanius continues in the next chapter with the Ebionites and Ebion:
Part 30. Epiphanius Against the Ebionites
2:7 Their origin came after the fall of Jerusalem. For since practically all who had come to faith in Christ had settled in Peraea then, in Pella, a town in the 'Decapolis'10 the Gospel mentions, which is near Batanaea and Bashanitis—as they had moved there then and were living there, this provided an opportunity for Ebion.
2:8 And as far as I know, he first lived in a village called Cocabe in the district of Qarnaim—also called Ashtaroth—in Bashanitis. There he began his evil teaching—the place, if you please, where the Nazoraeans I have spoken of came from.
2:9 For since Ebion was connected with them and they with him, each party shared its own wickedness with the other. Each also differed from the other to some extent, but they emulated each other in malice. But I have already spoken at length, both in other works and in the other Sects, about the locations of Cocabe and Arabia.
3:1 And at first, as I said, Ebion declared that Christ is the offspring of a man, that is, of Joseph.
The prophecy by Christ that caused all the disciples to move to Pella might well be the one recorded in the Gospel of Matthew, which was apparently the favored Gospel of the Ebionites:
Matt.24
[4] And Jesus answered and said unto them, Take heed that no man deceive you.
[5] For many shall come in my name, saying, I am Christ; and shall deceive many.
[6] And ye shall hear of wars and rumours of wars: see that ye be not troubled: for all these things must come to pass, but the end is not yet.
[7] For nation shall rise against nation, and kingdom against kingdom: and there shall be famines, and pestilences, and earthquakes, in divers places.
[8] All these are the beginning of sorrows.
[9] Then shall they deliver you up to be afflicted, and shall kill you: and ye shall be hated of all nations for my name's sake.
[10] And then shall many be offended, and shall betray one another, and shall hate one another...
I wonder if this isn't partly a reaction to Josephus' claim that Vespasian was the leader that was supposed to come out of Judea?
Whether the history of the first Christians settling in the Pella area is accurate or not I don't know. It may have been a legend that had become history by Epiphanius' time. But that an orthodox Christian writer had the first Christians settling in the area from whom the Nazoraeans and Ebionites originated seems significant to me.