“He had still one other,
A beloved son.
He sent him
‘They will respect
ἔτι ἕνα εἶχεν, υἱὸν ἀγαπητόν· ἀπέστειλεν αὐτὸν ἔσχατον πρὸς αὐτοὺς λέγων ὅτι Ἐντραπήσονται τὸν υἱόν μου.
The sending of the beloved son of the landowner in this parable can be found in Matthew, chapter 21:37, and Luke, chapter 20:13, almost word for word. Mark said that this landowner had his own beloved son (ἔτι ἕνα εἶχεν, υἱὸν ἀγαπητόν). Finally, he was going to send him to these wicked tenants (ἀπέστειλεν αὐτὸν ἔσχατον πρὸς αὐτοὺς). He said (λέγων) to himself that they would respect his son (ὅτι Ἐντραπήσονται τὸν υἱόν μου). This story is becoming clearer now.