Shall ye begin (arxesthe). Future middle, though Westcott and Hort put arxēsthe (aorist middle subjunctive of archomai) and in that case a continuation of the aph' hou construction. It is a difficult passage and the copyists had trouble with it.
In thy presence (enōpion sou). As guests or hosts or neighbours some claim, or the master of the house. It is grotesque to claim credit because Christ taught in their streets, but they are hard run for excuses and claims.