He starts out with the false premise that God made Mother Teresa a Saint, but that was not the case. We are all put here on this earth with free will to chose our path, albeit in different situations. That was the path Mother Teresa chose for herself, which is why the Pope recognizes her as a Saint. One would assume that God views her in a positive light as well, but God neither made her a Saint nor is God the one making her a Saint.
The priests guilty of sins against children chose their own path and will have to answer to God, just a Mother Teresa will have to. According to teachings the outcomes will be quite different for the priests from that of Mother Teresa. This author, as well as, every other soul that departs this earth will face their judgment day too.
Incorrect. Catholic theology teaches that God is the one who makes someone a saint. The Pope simply affirms this on earth after the Catholic Church investigates the person's life. There are many more saints in heaven that those who have been officially proclaimed as such on earth, including countless saints known only to God.