Sorry, misunderstood. All are/were “able not to sin.” While man in Heaven has free will, he doesn’t sin. It is analogous to “Can God murder?”
Since God is omnipotent, He “could,” but it is not His nature. So for all intents and purposes, the answer is no.
As the soul in Heaven, “could” choose to sin, but because of the nature of Heaven, doesn’t.
Adam pre-fall was able to sin and able not to sin. Post-fall, only the regenerate man has the same capabilities. The unregenerate man does not have the ability not to sin, since without faith, it is impossible to please God, and the faithless do not seek God. And in Heaven, man will not have the ability to sin.
Man’s will is fettered by his nature, and also by the Will of God. Man will always choose what his nature thinks is the right thing to do at that time.