In that Tafsir, it says hypothetically speaking, as in what if situation, God could (it doesn’t say should) beget a Son, meaning it is possible for Him if He so wishes, but the Tafsir says that ultimately, God did not beget a Son.
Sure. A major claim of the Catholic Church, is that she possesses Sacred Tradition and Apostolic Succession; which is equivalent to the Hadith and Sunnah in Islam.
You must keep in mind, you would not pick up a Quran, and interpret it however way you want.
There are many books in the Bible, the books of the New Testament were written by some of the Apostles of Christ; the Twelve, and the Seventy. These men either directly knew and were chosen by Christ Himself to spread the Gospel and Baptise in the Name of the Father, the Son, and the Holy Spirit, or, they directly knew the aforementioned men and also had authority to do what they did.
Obviously, the authors of the New Testament, knew what they were writing about, it is not up to someone two thousand years later to believe their own, differing interpretation holds more authority. The authors of the New Testament, and the rest of the Apostles, passed on their knowledge to whoever they deemed worthy to succeed them. These Traditions in turn, are recorded in writing by the Church Fathers, the earliest of whom would be equivalent to the Salaf in Islam.