Q:

John 9:18 - was Jesus praying 'alone' and his disciples in the room? 

και εγενετο εν τω ειναι αυτον προσευχομενον καταμονας συνησαν αυτω οι μαθηται
Luke 9:18 - TR (Stephens, Beza, Elzevir and Scrivener are all identical.) 
And it came to pass, as he was alone praying, his disciples were with him: [KJV 1769]

Do the verbs ειναι, προσευχομενον and συνησαν tell us whether Jesus was in the same location as the disciples - he praying, they perhaps not - or do they imply that the disciples entered that location whilst Jesus was at prayer ? 
It intrigues me that he could be in the same room, perhaps - or in the came location - and be praying whilst others were around him, yet not be disturbed by their presence. 
'Alone' could mean that he alone was praying.  Or it could mean he was alone, then others joined him. 
What do the verbs imply ? 

A:

The verbs in Luke as well as the rest of the verse are rendered quite well by the KJV and most others.   The verb for praying is accusative masculine singular.   The phrase in the Greek translated "alone" is "kata monas" which is literally, "according to one".   (Compare the same use of the phrase "kata monas" in Mark 4:10 where Jesus is alone, apart from the multitude but with His disciples.) 
The idiom of this could easily be (and obviously was) that while Jesus was praying, He was the only one speaking but the disciples were with Him in a private location.   Presumably, this meant that they were sharing a little prayer time and perhaps taking it in turns to pray.   That is, they were having what would be called in modern terms a private prayer meeting. 
This is confirmed by the next word, "sunesan" is correctly rendered, "were with" and is plural.   Thus we have "paying" is singular and "were with" is plural. 
Jesus set a wonderful example of having private devotions and prayer meetings in both small groups (as here) and also being completely alone where he would sometimes spend the whole night in prayer.