Unfortunately, as@billsherman has said this is a rabbit hole. He is right. Not only are we are off topic but we are just repeating our points. This will be my last post addressing this topic.
So
they (
Identified as Cleopas and an unknown companion) set out at once and returned to Jerusalem where
they (Identified as Cleopas and an unknown companion) found gathered together the eleven and those with them
who were saying , (
The who is the apostles. Structurally both in Greek and in English Who refers back to the Apostles and those with them. And what are the Apostle and those with them saying?)"The Lord has truly been raised and has appeared to Simon!“Then the
two (
The narrative returns to Cleopas and an unknown companion) recounted what had taken place on the way and how He was made known to them in the breaking of the bread.While they were still speaking about this,He stood in their midst and said to them, “Peace be with you.”
But **they **were startled and terrified and thought that
they were seeing a ghost.
It is confusing because the writer continually uses the pronoun they without any other identification.
To follow your scenario each
they would refer to Cleopas and an unknown companion which would make them believe and at the same time be an unbeliever. This of course is not true just as your objection " the eleven apostles simultaneously believed and not believed Jesus had risen” is not true
Can you say with certainty there was not another disciple, not apostle, of Jesus named Simon?
Scripture doesn’t drop in random names of people.
Yeah I can say with certainty that Simon was Peter, not only does Paul makes that clear but other Scripture does as well. The only time Simon is mentioned is referring to Peter. If another Simon is meant, he is so identified.