Thank you for giving me an opportunity to speak on this, because it will probably be edifying to an actual Calvinist.
A more full quote from that first reference is...
"These are the great works of the Lord, sought out according to all His pleasure,(6) and so wisely sought out, that when the intelligent creation, both angelic and human, sinned, doing not His will but their own, He used the very will of the creature which was working in opposition to the Creator's will as an instrument for carrying out His will, the supremely Good thus turning to good account even what is evil, to the condemnation of those whom in His justice He has predestined to punishment, and to the salvation of those whom in His mercy He has predestined to grace. For, as far as relates to their own consciousness, these creatures did what God wished not to be done: but in view of God's omnipotence, they could in no wise effect their purpose. For in the very fact that they acted in opposition to His will, His will concerning them was fulfilled. And hence it is that "the works of the Lord are great, sought out according to all His pleasure," because in a way unspeakably strange and wonderful, even what is done in opposition to His will does not defeat His will. For it would not be done did He not permit it (and of course His permission is not unwilling, but willing); nor would a Good Being permit evil to be done only that in His omnipotence He can turn evil into good."
This is not actually double predestination, because it is actually the choice that someone made through their free will that was predestined to damnation, not the one making the choice.
Besides that, Augustine actually wrote a book specifically on the subject of free will which makes it clear that he does in fact believe it.
A more full quote from the second is
"And these we also mystically call the two cities, or the two communities of men, of which the one is predestined to reign eternally with God, and the other to suffer eternal punishment with the devil."
In the context of the book, the two cities are a choice. One between the eternal truth of God and the other the pleasures of the transient world.
This is not actually double predestination.
Calvinistic double predestination is based on the idea that there is no free will, because God's sovereignty makes it impossible.
That is not what the church has ever taught. Neither is what Augustine ever taught.
That said, even if Augustine did teach this, he is one of many church fathers, and it isn't really altogether strange for some of them to hold views that ultimately were not accepted by. the whole church.
Also, and I think it is worth mentioning... Augustine did not know Greek, he knew Latin. The New Testament was written in Greek, not Latin. In fact, because Augustine was working with a Latin translation, he is at least known by the Church to be in error about one thing in particular, and this has had a big impact on the west. He believed that every human shares the guilt of the garden of eden. The Church doesn't teach this, but that we inherited the mess caused by it, not the guilt. This error is actually rooted in translation issues between Greek and Latin.