I think you could replace with multiple expressions separated with "or" - you'll want to test this, of course, and verify it works in client prior to trying in browser.
not(my:MasterLaborPerson = current()/preceding-sibling::my:RoomingTable/my:Occupant1)
OR
not(my:MasterLaborPerson = current()/following-sibling::my:RoomingTable/my:Occupant1)