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No, I am not a priest.

My brother did what your friend is in danger of doing: he left the true Faith and became Antiochian Orthodox, dragging his entire family with him — including one of my godchildren. His excuse was the current crisis, but the reality was that he never established the family Rosary in his home and was (and remains) puffed up with pride. To think we can stand tall amid the storms that rage today without the Rosary is the height of arrogance and self-reliance.

At the time of his apostasy, it took all of us completely by surprise — he did everything, as much as possible, in secret. I also knew very little then about Orthodoxy or the early Church. My attitude was simply, "They’re schismatic and not worth my time."

My brother made many bold claims — that "the papacy as we know it today didn’t exist in the first millennium," that "the early Church was structured around bishops and patriarchates, not Rome," and that "doctrinal decisions were made by councils, not by the pope."

That prompted me to dive deeply into the topic, studying and researching the claims of Orthodoxy, reading ancient texts, and learning everything I could about the first thousand years of Christianity. I purchased dozens of books, studied the Patriarchs of Constantinople, examined the first seven/eight councils, explored the various East–West schisms (Acacian, Photian, and others), and reviewed the doctrines and internal differences among the sixteen or so "autocephalous" Orthodox churches.

What I discovered was that these claims were not merely mistaken — they were demonstrably false. The truth of the Catholic Church’s claims shines as brightly in the earliest centuries as it does today, expressed most clearly in Pastor Aeternus from the First Vatican Council. Even in the acts of the councils — from Ephesus and Chalcedon through later Councils of Constantinople — the authority and primacy of the Apostolic See are unmistakably clear.

In fact, nearly all of the Orthodox arguments about the papacy and early Church structure are borrowed from Anglican sources. In the 19th century, the Oxford Movement arose among Anglicans who, after reading the Fathers, realized the early Church was thoroughly Catholic. Confronted with this, they faced a choice: return to the True Church or invent excuses for remaining in schism. Most chose the latter. Out of that came various arguments — centered on incidents involving St. Cyprian, Popes Vigilius and Honorius, and others — meant to portray the early Church as a loose federation of autonomous bishops rather than a unified body under Peter’s successor. Modern Orthodox "apologists" simply inherited and repeated these same arguments, often with little refinement.

Every one of these objections was answered decisively in the 19th century by Catholic theologians and historians who confronted them with historical fact, reason, logic, and the actual writings of the Fathers and councils. They demonstrated beyond doubt that the Anglican (and now Orthodox) claims were assertions built on selective reading and conjecture rather than truth.

I went back to the sources myself, reading the writings of the early popes directly — through Patrologia Latina and many other collections — to see what these men actually said about the Church and their office, without the filter of later biased historians and commentators.

This led me to establish The See of Peter, a project to provide solid translations of papal writings from the earliest centuries. When one reads these texts plainly, without commentary, the truth becomes obvious: the popes knew exactly who they were and what authority they possessed — and so did everyone else. They did not go about declaring "I am in charge"; they simply exercised their office, and those subject to them — even when disobedient — never denied their right to do so. Nowhere in the early Church do we find anyone asking, "Who made you pope?" or "What gives you the right to speak for the Church?" There were rebellions, yes — but never denial of Rome’s authority.

You're quite welcome.

It's crucial that he pray the Rosary with attention, devotion, and piety/meditation.  And I would absolutely recommend all 15 mysteries, each day.

If he does that, and sticks to it, her "Immaculate Heart will be [his] refuge and the way that will lead [him] to God."