Regarding Gregory – a piece of very sloppy scholarship here be a non-expert – I’m going to quote Wikipedia -
en.wikipedia.org/wiki/Gregory_of_Nyssa
It is generally agreed that Gregory believed in universal salvation or resurrection. In the Life of Moses, he writes that just as the darkness left the Egyptians after three days, perhaps redemption ἀποκατάστασις] will be extended to those suffering in hell γέεννα].This salvation may not only extend to humans; following Origen, there are passages where he seems to suggest (albeit through the voice of Macrina) that even the demons will have a place in Christ’s “world of goodness”.Gregory’s interpretations of 1 Corinthians 15:28 (“And when all things shall be subdued unto him …”) and Philippians 2:10 (“That at the name of Jesus every knee should bow, of things in heaven, and things in earth, and things under the earth”) support this understanding of his theology.
However, in the Great Catechism, Gregory suggests that while every human will be resurrected, salvation will only be accorded to the baptised.While he believes that there will be no more evil in the hereafter, it is arguable that this does not preclude a belief that God might justly damn sinners for eternity.Thus, the main difference between Gregory’s conception of ἀποκατάστασις and that of Origen would be that Gregory believes that mankind will be collectively returned to sinlessness, whereas Origen believes that personal salvation will be universal.
OK – I have seen this discrepancy between Gregory’s earlier writings and his Great Catechism referred to before by Orthodox scholars who want him for the ECT camp (they make a distinction between the heterodox youthful Gregory and the orthodox ‘mature ‘Gregory’ of the Great Catechism). My two pence worth in this debate – and its just a suggestion – is that Gregory in the Great Catechism is presumably writing for new/immature Christians. And if his teaching about universalism is less certain here than in his other writings one reason could be that like Origen he held to a notion of ‘double truth’ – namely, that universalism should only be fully disclosed to mature Christians already schooled in Christian virtue. Perhaps I’m talking rubbish