YOu have completely missed the point that the Romans, did know the Bible. They were not idiots, Josephus by himself is probably more qualified about jewish than nay modern scholar, simply because he was there, and had access to material we can only dream of. Living at the time he would have seen and heard things that have been lost through time and our modern shcolars can never hope to know. TO continue on and on hardly disproves the possibility that the Romans wrote the gospels. They were educated, they had the resources.
They knew which scriptures to use and promote and which to leave out. We all know that Mt badly twists many scriptures like the riding on the two donkeys and others, because he must find parallels to prove jesus in prophecy even if the references are wrong and dishonest. We have the same dishonesty in the twisting of Micah 5 which supposedly predicts the Messiah will be born in Bethlehem. The gospels writers tried really hard to impress prophecy on the reader that i will agree. They tried their best, it would be hard to imagine anyone else doing better with what they had to work with.
The fact that jews rejected Jesus today, shows that he did not match the criteria of the prophecies but the authors used the text anyway.