“leaders.” The Hebrew is baal, in this context likely the leaders or landowners.

“Beth-millo.” Beth-millo could be another site location nearby Shechem, or it could possibly be another area of Shechem, such as a specially built-up or fortified area of Shechem.

“oak of the pillar.” The “pillar” seems to be something “set up,” and associated with a place, not just a single pillar. So the oak of the pillar would have been in the general area of the pillar, or thing that had been set up.