Mark 16:14

And afterward he was manifested unto the eleven themselves as they sat at meat; and he upbraided them with their unbelief and hardness of heart, because they believed not them that had seen him after he was risen.

This verse establishes, by its repetition of it, the fact that the eleven apostles were the persons meant by the pronoun "them," not only here but completely to the end of this Gospel, there being utterly no grammatical device known to man by which any other antecedent for this pronoun appears anywhere in the whole passage. The last "them" in this verse, of course, is the lone exception and has reference to the "them" in Mark 16:12-13.

Upbraided them with their unbelief ... The eleven apostles were unbelievers regarding the fact of the resurrection, at first; and their reluctance to believe the two who came back from Emmaus and Mary Magdalene may have stemmed partially from human pride. After all, they had frequently engaged in discussions of who would be greatest in the kingdom of God; and, on the very first day of the resurrection, the Lord had appeared to once-notorious Mary and to two nameless disciples not even belonging to the sacred company of the apostles. No wonder they could not believe it. It was not that they did not believe that Jesus was alive, Peter and John having already seen the convincing evidence in the tomb early that morning. It was simply that they could not believe that Jesus had appeared to THOSE people! All this is implied in the next clause.

And hardness of heart because they believed not them that had seen him ... Ah, there it was! Mark had similarly recorded another instance of the Twelve's hardening of their hearts in Mark 6:52. On that occasion also, the Twelve were not in full harmony with the will of God, just as in the case of the eleven here.