Complex sentence: The Family had always owned the adjoining property, which they tennanted out, after William's hospitalisation the tennants become the caretakers of the Straw's house, and after William's death in 1990 inteherited both properties.
Split into simpler sentences: The family had always owned the adjoining property, which they rented out. After William's hospitalisation the tenants become the caretakers of the Straw's house, and after William's death in 1990 inherited both properties.