One poster mentioned a restraining order...i like that but would say if you really want to

Give him a wake up call on his behavior...i would ask EVERYONE that was present to request restraining orders and or tell him or you sister he is no longer welcome in there presence or on their property.

It doesnt matter if he might never go to their homes its the uniform exclusion and voiced repugnance of his actions that might make him take stock of his disgusting behavior.