While the Church Fathers believed Adam and Eve were historical, that does not mean they believed the account of Genesis chapter 3 was likewise historical.
For instance, canonized Catholic saint Gregory Nazianzen (c. 329-390) wrote that the narrative of the Fall was set in simplified language, detailing that the Tree of Knowledge was but a symbol for "contemplation" (which in Roman Catholic theology is a type of wordless prayer that brings humans in mystical communicative intercourse with God).
There are other historical personages which Scripture often sets into parable type narrative. The prophet Jonah is supposed to be a historical prophet according to Jewish history, but the Biblical book is written as a humorous moral lesson with details impossible to reconcile with reality even by religious standards. The Hebrew Daniel is supposed to be historical, a hero who lived faithfully as a Jew among Gentiles before the Babylonian exile, but the "prophet Daniel" of the book in Scripture are but legends of him set in apocalyptic tableau (which is why Daniel is not considered one of the historical prophets in Judaism). Ruth is also a historical figure, but her narrative was likely invented during the time of Ezra and Nehemiah during the foreign wives controversy.
Jesus of Nazareth often used fictional narratives called "parables" to pass on what are viewed as religious truths. Some of the characters may be real personages known to the culture of the period (such as the "Lazarus" who dies alongside a nameless rich man--a poor beggar who would likely not be known by a name for any reason except the possibility that he was well-known in that era perhaps). The stories are complete fiction, but the situations are real, often drawing from real things common to first-century Jewish life with axioms that have practical value and universal applications in some instances, again all this despite their fictional nature.
Lastly, it is a common mistake of Jehovah's Witnesses to draw the conclusion that God requires the death of an Adam like figure to ransom humanity as JW theology claims God must be appeased by human sacrifice. This is a late interpretation, confined mostly to American religious movements that arose from the Second Great Awakening era. This idea has no commonality with the centuries-old view which is well established not merely in theology but in countless paintings, poetry, and even song throughout the centuries.
This older Christian exegesis is that Adam and Eve are also saved by Christ's death, and even the Church Fathers often speak of Adam being the first to be released from death by Christ. Christ is "Adam" in nominal Christology not because his death is an equivalent payment to balance the scales of justice (which is a Watchtower teaching) but that Christ becomes the new Father of the human race. In Orthodoxy and Catholicism, as well as Anglicism and even among some Lutheran teachers, Mary becomes the new "Eve" for humanity in the same manner.