Dear Joe,
Thank you for providing the link on St. Gregory's life. My Roman Catholic apologist friends would agree that St. Gregory's Dad was a bishop. But they would argue that he and his wife (Gregory's mother) became celibate once he was ordained to the priesthood. Hence, Gregory must have been conceived before his father was ordained a priest.
Again, the crux of the Roman Catholic argument is this: in the early Church, when a married man was ordained a priest, he and his wife ceased having sexual relations. To refute this argument, we must provide well-documented examples to the contrary. Are there any sources that indicate that St. Gregory was conceived after his father was ordained a priest? If we could find such a source, it would go a long way towards blowing the extreme RC position out of the water.
Anthony