The plural of Bews is Bewses, as Joneses is the plural of Jones, as in "keeping up with the Joneses". There is one Bob Bews in this town. There are two Bob Bewses in this town.
Bew's means that one Bew possesses something, as in Bob Bew's hat is in the ring, i.e., the hat of Bob Bew is in the ring.
Bewses means that more than one Bews possesses something, e.g., those are the Bewses' horses, i.e., the horses belong to the Bewses.
When referring to the Bewses, Bews' and Bews's mean nothing.