I have never interpreted the Fatima Prayer as referring to those most grievous (and serial) sinners who wantonly and irrevocably chose to implement the devil’s most grievous intentions while on earth...true agents of Satan...no more capable of genuine repentance than is Lucifer himself. To say that they are — other than solely out of a fear of eternal punishment — sounds like bleeding-heart wishful thinking to me. Gosnell and others on your list essentially passed through the one-way gateway to hell while still living and breathing on this earth.
The problem with your line of thinking is that it places the burden of salvation on the sinner, not on God. Gosnell or whoever doesn’t have to be capable of repentance on their own, because, if it happens, it will happen through the power of God, not through their own efforts. Remember, sometimes God chooses to step in and change the hearts of even the most despicable men, not because they deserve it, but because it demonstrates the glory, mercy, and sovereignty of God.
"In hope, the Church prays for "all men to be saved." (Catechism link)
and
This is not Universalism; it does not require, or even hint, that Hell might be empty or have no inhabitants except Satan and his bodiless hordes of demons.
Hell is a hot possibility for anyone, and a terrifying one.
That is why we pray without ceasing. You for me, me for you, all of us for the most despicable sinners --- save them, Lord, we pray.
"Especially those in most need of Thy mercy."