Here are links to some resources from this website that provide information about the history and development of the Four Gospel accounts of the New Testament.
A section of Notes from FIVE COLUMN: The Synoptic Gospel that provides a brief overview and description of the Four Gospel accounts of The Life of Jesus Christ that are the first four Books of the New Testament.
A Chart comparing the major differences between the Four Gospel accounts of The Life of Jesus Christ that open the New Testament.
A Nine Part Video Series that explores the history and development of the Four Gospels of the New Testament, including the synoptic overlap and the merged harmonies of their texts. (Audio and Video Series)
An Appendix of FIVE COLUMN: The Synoptic Gospel that shows which verses from the Four Gospels are part of a parallel set, and The Synoptic Gospel Scene which includes them. Looking up this Scene Reference in the FIVE COLUMN book will show how the verses from the original Gospels are related, and how they were combined to produce the text of The Synoptic Gospel.