Well, even then, we have to look at their rationale for believing what they believe. Did they refer to history? To scripture? If the latter, how valid are their exegesis?
Church Fathers are HUMAN and are not infallible. We respect them for their wisdom, but that does not mean that we read them without discernment.
And even if we look at the early church fathers we see DISAGREEMENT among them regarding to status of Mary as perpetual virgin and even when they do agree, their explanation for the disagreement conflicts with one another.
For instance, the early church father Tertullian denied that she was a perpetual virgin.
Then, over a hundred years later, church father Jerome argued that she was, and attempted to explain away the references to Jesus’ “brothers and sisters” in the New Testament by assuming that they were actually cousins. Did he explain away the term — ADELPHOS?
Then, even later, the church father Epiphanius, while agreeing with Jerome that Mary was a perpetual virgin, tried to explain away the “brothers and sisters” mentioned in scripture by assuming that they were children of Joseph from a former marriage.
So, for those who want to establish doctrine based on post-apostolic “tradition”, which view of Mary is to be accepted?
When three different church fathers give three different views, which one is to be followed?
The safest course is for SCRIPTURE TO SPEAK FOR ITSELF.
If the scriptures speak for themselves, the obvious conclusion is that while Mary was a virgin until Christ’s birth, she had other children later.
The New Testament writers were familiar with the Greek terms for “cousin” and “relative”. They used them. When referring to Jesus’ “brothers and sisters”, though, they used terms with a primary meaning of SHARED PARENTAGE.
Since people who want to believe that Mary was a perpetual virgin cannot find evidence for that belief in the New Testament, they try to find evidence in material written LONG AFTER Mary and the apostles had died.
So the New Testament evidence against Mary being a perpetual virgin is overlooked, as is the testimony of men like Tertullian, who didn’t support the doctrine.
People who want to believe that Mary was a perpetual virgin search through the writings of the church fathers until they find something they agree with, then they READ THAT DOCTRINE BACK into the New Testament, even if the New Testament actually doesn’t support it.
Either that, or people who do not want to accept the fact that Mary WAS a perpetual virgin READ THAT DOCTRINE BACK into the New Testament, even if the New Testament actually doesn't support it. Once you buy into the error of private interpretation, you can ascribe to any theory you want to and say "That's what the Bible says, and if you don't agree with me, you're wrong."