The "they" include the two disciples sent over earlier to prepare the meal (14:13-14). These two stayed there, so the meal included at least 15 people--the Twelve, Jesus, and these two disciples--who are the brothers of Jesus named James (Jacob) and Jude (Judas). That there were more than Jesus and the Twelve at the meal is betrayed (sorry for the pun)in 14:20, where Jesus states that the betrayer is one of the Twelve. If only the Twelve had been there, Jesus would have stated that the betrayer is one of you. The brother of Jesus named James is the mysterious Beloved Disciple of John, who first appears at the Last Supper (John 13:23-26), and the brother of Jesus named Jude is the Jude (not Iscariot)--who according to John 14:22 was also present at the Last Supper. On James being the Beloved Disciple, see The Jesus Dynasty (pp. 206-207), where James D. Tabor states, "Later, just before Jesus' death, the gospel of John tells us that Jesus put the care of his mother into the hands of this 'disciple whom he loved' (John 10:26-27). How could this possibly be anyone other than James his brother, who was now to take charge of the family as head of his household?" The BD (i.e., James) had the place of honor at the meal, so he had been chosen by Jesus to succeed him as the head of his movement--which is why James did in fact become the leader of the earliest Jesus group in Jerusalem. Mark hides all this because it falsifies his claim that Peter had been the legitimate successor to Jesus as the head of his movement (So, in 16:7, Mark has the young man in the tomb speak of "his disciples and Peter" because, in Mark's eyes, Peter had been elevated from the status of disciple to the status of leader of the movement upon the death of Jesus.) Also, in 15:40, Mark speaks of a Mary the mother of James the Lesser and of Jude. This is Mary the mother of Jesus, but, since he was now dead and since it was James and Jude who went ahead to preapare the meal, Mark speaks of her as being the mother of this James and of this Jude. Mark mockingly gave James the brother of Jesus the title of "the Lesser" because he was pro-Peter and anti-James.