But those tenants said to one another, ‘This is the heir. Come, let us kill him, and the inheritance will be ours.’
Mark 12:7

The only way this scheme would work is if the son was an only child and the tenants were close relatives. Otherwise, they would have no expectation of receiving an inheritance from his death. Per God's Law, inheritance in the Land of Israel must always go from father to son or to daughter if he has no sons. If the man has no children, then his brothers or uncles will be his heirs.

The tenants in this parable are the Pharisees and other religious leaders of 1st century Judea. The vineyard is the people of Israel, including the Jews.