Here is the original Greek:
10
καὶ εá½�θὺς ἀναβαίνων á¼�κ τοῦ ὕδατος εἶδεν σχιζομÎνους τοὺς οá½�Ï�ανοὺς καὶ τὸ πνεῦμα ὡς πεÏ�ιστεÏ�ὰν καταβαῖνον εἰς αá½�τόν:
11
καὶ φωνὴ á¼�γÎνετο á¼�κ τῶν οá½�Ï�ανῶν, Σὺ εἶ á½� υἱός μου á½� ἀγαπητός, á¼�ν σοὶ εá½�δόκησα.
12
Καὶ ε�θὺς τὸ πνεῦμα α�τὸν �κβάλλει εἰς τὴν ἔ�ημον.
13
καὶ ἦν á¼�ν τῇ á¼�Ï�ήμῳ τεσσεÏ�άκοντα ἡμÎÏ�ας πειÏ�αζόμενος ὑπὸ τοῦ Σατανᾶ, καὶ ἦν μετὰ τῶν θηÏ�ίων, καὶ οἱ ἄγγελοι διηκόνουν αá½�Ï„á¿·.
First off: notice εἶδεν means "he saw." As in, just Jesus saw, not everybody saw, because it was a vision, not a physical event. Then a string of "and" connectors indicates that the voice was part of Jesus' vision, not a physical voice.
Just looking at the Greek as an amateur scholar, it seems indisputable to me that "he saw" is singular. That means that Jesus saw the heavens open, and no one else saw it. That means that the Bible is describing a visionary event, not something physical that could be seen by any eye-witness. That's *my* interpretation.
However, another interpretation would be that something literally happened with the sky, something was visible and tangible to all onlookers. Maybe *everybody* saw the sky open, but the Gospel use a singular verb form for some reason.
A third interpretation is that the whole thing is fictional and must be understood as literary fiction, but the argument for that seemed to be completely indecipherable to me. It may have relied on something that requires a Master of Fine Arts.
I think it's possible to leave aside the issue of fact and fiction so that we can focus on the best way to translate the text. Is the form of "he saw" meant to indicate that *only* one person saw?