Duplicate important resources
Provide multiple feeding, drinking, resting, hiding, scratching and toileting locations. Spread them out so one cat cannot guard every route or resource.
Introduce through stages
Begin with separate safe areas. Work gradually through scent, sound and controlled visual access before direct contact. Move at the pace of the least comfortable cat.
Watch the quiet signs
Conflict is not always a fight. Blocking corridors, staring, displacement from resting places, hiding, spraying and changes in appetite or toileting can signal tension.
Get individual advice
Pain, illness and previous experience can affect social behaviour. Ask your veterinary team or a suitably qualified feline behaviour professional for help when tension persists.