The operative Greek phrase in John 17:12 is ὁ υἱὸς τῆς ἀπωλείας = the son of destruction.
The word υἱὸς (huios) is singular.
The word "perdition" or "destruction" translates ἀπωλείας and is used as a proper name for Satan in Rev 9:11. Thus, "son of destruction" would refer to someone who follows Satan and his ways - see John 8:44.
Most understand this phrase to refer to Judas who betrayed Jesus and then suicided. Ellicott observes:
The term, "son of perdition," is a well-known Hebrew idiom, by which
the lack of qualitative adjectives is supplied by the use of the
abstract substantives, which express that quality. A disobedient child
is, e.g., "a son of disobedience;" other common instances are
"children of light," "children of darkness." A "son of perdition" is
one in whose nature there is the quality expressed by "perdition." The
phrase is used in Isaiah 57:4 to express the apostacy of the
Israelites (in English version, "children of transgression"). It
occurs once again in 2Thessalonians 2:3, of the "man of sin."
But the son of perdition … The term son was given by the Hebrews to
those who possessed the character described by the word or name
following. Thus, sons of Belial - those who possessed his character;
children of wisdom those who were wise, Matthew 11:19. Thus Judas is
called a son of perdition because he had the character of a destroyer.
He was a traitor and a murderer. And this shows that he who knew the
heart regarded his character as that of a wicked man one whose
appropriate name was that of a son of perdition.