His circle were the people that believed he was the lord.
Their vested interests were that they dedicated their lives to his message. They were hardly objective is my point.
The Gospels were not written to give a historical account of the events of Christ's life, they are apologetic narratives that contain a historical witness. The two Gospel writers that I understand to have been viewers of most of Christ's life and events were Matthew and John, Mark wrote for and traveled with Peter and so his testimony would not be considered as eyewitness. Luke was the closest to an objective account as he interviewed eyewitnesses and some of the apostles.
Luke did the best job of relating the events of Christ's life to historical timelines, this extended into the book of Acts.
If you understand that the Gospels were meant to convince hearers of the truth of Christ's life leading to His death and Resurrection, it is unreasonable to expect them to be objective. Sure there was emotion woven into their accounts, if I saw the miracles of Jesus and witnessed Him crucified and then alive again, I would not be objective and emotionless either, and I don't think you would be. I would place more value on what is truthful as opposed to what is more objective and this is the characterization of the New Testament, it is truthful.
Again however, I have to address the idea of a "vested interest", which means by the definition of the phrase, that the Gospel writers and the authors of the Epistles somehow had an expectation of a personal gain. This could not be further from what happened and the authors of these texts knew the only earthly reward for them was death and they were ready for that.
The only interest of any gain was life in heaven with God and the sole purpose of the texts in the New Testament was not for earthly gain but for eternal gain of life with God. And this gain was not one of self but to share the "good news" with as many people as possible so that the hearers would receive this eternal life. Case in point is in Acts chapter 8 where Simon the magician offered money to be able to impart the gifts of the Holy Spirit and Peter severely chastised him because the message of Christ is not for earthly gain but for eternal gain.
While attending university, I have studied the Old and New Testaments and in the text books used, each book of the Bible was examined separately and almost without fail there were textual and form criticisms of each book. The leading higher criticism of the OT of course was the Documentary Hypothesis in the 1700's and after it had run its course, many scholars, through archeological discoveries and study, have abandoned this criticism.
The NT has been harder for critics to prove as unreliable or untruthful in relation to the central eternal truths. As is fairly well known, the last few verses of Mark and the woman taken in adultery in John, may not have been part of the original autographs. It does not necessarily mean that the account of the woman taken in the book of John is not true, it just may mean that John did not pen the account. The determination of truthfulness is not in the accuracy of determining who penned what but rather, were the NT accounts God inspired and truthful?
"While we do not have the autographs (original writings) of the New Testament, nonetheless, the witness to the New Testament books is formidable. For example, there are some five thousand extant manuscripts that contain either the complete New Testament or portions of it.
Papyrus manuscripts. These manuscripts are old and an important witness. For example, the Chester Beatty Papyrus dates from the third century.
Uncial manuscripts. Approximately two hundred forty manuscripts are called
uncial manuscripts and are identified by
capital letters. Codex (meaning “book”

Sinaiticus contains all the New Testament and is dated a.d. 331. Codex Vaticanus contains most of the New Testament, is dated from the fourth century, and is considered one of the most important manuscripts. Alexandrinus, dated fifth century, contains all the New Testament except part of Matthew and is helpful in determining the text of Revelation. Others include Codex Ephraemi (5th century), Codex Bezae (5th-6th century), and Washington Codex (4th-5th century).
Minuscule manuscripts. There are some twenty-eight hundred
minuscule manuscripts that are written in
small letters usually in a flowing hand. They are normally not as old as uncial manuscripts. Some of the minuscules reveal a similarity of text-types and are referred to as a “family” relationship and are so categorized.
Versions. A number of early versions of the New Testament also help in understanding the correct text. Several
Syriac versions exist, among them Tatian’s Diatessaron (a.d. 170), the Old Syriac (a.d. 200), the Peshitta (fifth century), and the Palestinian Syriac (fifth century). The Latin Vulgate, translated by Jerome (c. a.d. 400), influenced the Western church. The Coptic translations (translated in the third century), including the Sahidic Version and the Bohairic Version, influenced Egypt.
Through the study of the Greek manuscripts as well as the early versions, textual critics have been able to determine the text that is substantially that of the original writings. It is evident that the hand of God has preserved the various texts through the centuries to enable scholars to collate them and reconstruct the text as closely as possible to the original writings."
The Moody Handbook of Theology.
Sometimes we lose track of the central message of the NT and that is Christ's death and resurrection as payment for our sins and in this truth, there is no contradiction or vagueness among the NT writers. When I die and stand before God and He asks me why He should let into heaven, my answer can not be "I believe the writers of the NT were truthful" or "I believe in the authenticity of the Bible". My answer must be to acknowledge and accept the truths of Christ's death and resurrection in all its demands and expectations.