Happy New Year Mystic,
You could never offend a true Catholic by asking about The Faith. St. Paul tells us to be ready to answer any and all things concerning Christ, so we gladly answer out of our love of Christ and you.
1. The Pope came to be this way: there has always been a spiritual leader of the House of Faith (the true religion given to mankind by God). In the very beginning, when man knew God personally from the day of his creation, Adam was the first "Pope" so-to-speak. Pope means Papa as in father, like our own, and even as in Abba Father, God the Father. Adam was the first Patriarch (also means Father). Abraham, Moses, Noah and other great men were also Patriarchs. They were responsible for leading those of the true monotheistic religion to God and to obeying God's commandments.
Before the arrival of the first Pope (Peter) and the founding of the Church, God used the High Priest of the Temple in Jerusalem as His Old Testament "Pope". The intention was to have the High Priest as the Pope of the New Testament also, but the Jews rejected their Messias.
The Jewish religion and their sacrificing priesthood of the Temple was the True Religion up until Christ. It was exclusively the True Religion. It ceased being the true faith after the Crucifixion of Christ and subsequently the destruction of the Temple in 70 A.D. by Titus the Roman. Then the true religion, the Catholic Church, went underground because of the great persecution as evidenced by the Catacombs.
When the Jews rejected Him, Jesus chose Simon Bar-Jonah to be the rock upon which He would build His Church (Matt. Chap. 16). After Peter died, Linus was the second Pope then Anacletus, Clement I, Evaristus, Alexander and so it was continued until this day. You can visit any secular encyclopedia and follow the succession of Popes since Peter (all 265 of them) up to and including Benedict XVI.
2. The orders of the Church are religious orders. The concept of religious life goes back to the Old Testament where the Carmelites hold the tradition that their order, the oldest, dates back to the prophet Elias who lived on Mt. Carmel. The purpose of religious orders is to more closely imitate Christ and to follow Him in the spirit of Matt. 19:29: "And every one that hath left house, or brethren, or sisters, or father, or mother, or wife, or children, or lands for my name's sake, shall receive an hundredfold, and shall possess life everlasting."
And also: "Jesus saith to him: If thou wilt be perfect, go sell what thou hast, and give to the poor, and thou shalt have treasure in heaven: and come follow me." Matt. 19:21 And again: "If any man will come after me, let him deny himself, and take up his cross, and follow me." Matt. 16:24
Those in religious orders give up everything to follow Christ as did the Apostles. The three main orders are the Carmelites, the Dominicans and the Franciscans, although there are many other religious orders such as the Jesuits, Redemptorists, etc.
I'm not sure what you mean by branches or denominations in the Catholic Church, so I'll wait for some specifics or examples.
3. The term brother for the Jews is not as specified as in English or other Romance languages. When a Hebrew called someone his brother, it simply meant there was a relation such as cousin, nephew, uncle, etc. This is true even today. Naming specific relatives is purely a Western designation in our languages. The Old Testament is replete with examples.
Just for the record, no Christian ever denied that Mary was always a virgin (before and after Christ's birth). This would include any and all of the Reformers, including Martin Luthor and Henry VIII. We do not see an attack on Mary's perpetual virginity until relatively recent times.
But the most important reason for Mary's perpetual virginity is that she is the Mother of God. How could such a mother NOT be a virgin? The prophecies of the Old Testament refer to a virgin conceiving a child (Who is the Messias). "Therefore the Lord himself shall give you a sign. Behold a virgin shall conceive, and bear a son, and his name shall be called Emmanuel" (meaning God with us). Isaias 7:14
The perpetual virginity of Mary is singular. There will never be another woman like The Virgin Mary, just like there could never be another Eve. Mary is the second Eve - she righted what was wronged by the fall of Adam and Eve. She bore the Messias.
Merry Christmas!