OP: Are there any more details about what happened here [Mt 27:52]?
And the graves were opened; and many bodies of the saints which slept arose, Mt 27:52
First, it's important to note that Christ was the first, then came the first fruits.
And came out of the graves after his resurrection, and went into the holy city, and appeared unto many. Mt 27:53
Who are they and is this mentioned elsewhere?
Ignatius short recension Letter to the Magnesians, which is generally accepted as authentic.
...by which mystery we have obtained faith, and therefore endure, that we may be found the disciples of Jesus Christ, our only Master—how shall we be able to live apart from Him, whose disciples the prophets themselves in the Spirit did wait for Him as their Teacher? And therefore He whom they rightly waited for, being come, raised them from the dead.
Who might they be?
Your father Abraham rejoiced to see my day: and he saw it, and was glad. John 8:56
[psalm of David] Therefore my heart is glad, and my glory rejoiceth: my flesh also shall rest in hope. For thou wilt not leave my soul in hell; neither wilt thou suffer thine Holy One to see corruption. Psalm 16:9-10
And these all [in Hebrews 11], having obtained a good report through faith [like Abraham and David], received not the promise: God having provided some better thing for us, that they without us should not be made perfect. Heb 11:39-40
Here is another Ignatian letter to the Trallians (longer recension).
By those in heaven I mean such as are possessed of incorporeal natures; by those on earth, the Jews and Romans, and such persons as were present at that time when the Lord was crucified; and by those under the earth, the multitude that arose along with the Lord. For says the Scripture, “Many bodies of the saints that slept arose,” their graves being opened. He descended, indeed, into Hades alone, but He arose accompanied by a multitude; and rent asunder that means of separation which had existed from the beginning of the world, and cast down its partition-wall.
Lastly, Irenaeus also mentions this event.
This event [floating iron] was also an indication of the fact, that when the holy soul of Christ descended [to Hades], many souls ascended and were seen in their bodies. Fragments From the Lost Writings of Irenaeus XXVIII
Further, Clement of Alexandria mentions this event.
If, then, He preached only to the Jews, who wanted the knowledge and faith of the Saviour, it is plain that, since God is no respecter of persons, the apostles also, as here, so there preached the Gospel to those of the heathen who were ready for conversion. And it is well said by the Shepherd, “They went down with them therefore into the water, and again ascended. But these descended alive, and again ascended alive. But those who had fallen asleep, descended dead, but ascended alive.” Further the Gospel says, “that many bodies of those that slept arose,”—plainly as having been translated to a better state. There took place, then, a universal movement and translation through the economy of the Saviour. The Stomata Book VI Chapter VI Paragraph VI
So, to answer the OP, Christ rose first from the dead, followed by first fruits of particular OT saints who lived/died in faith of a Redeemer. This is mentioned in Matthew's Gospel and subsequently by Ignatius and Irenaeus and Clement of Alexandria.
PS. The reality of this refers to the shadowing of the barley harvest at Passover.