Complex sentence: According to church records his parents were William Jamison (or "Jameson") and Mary Jamison (nee Fisher), and his forebears had made their living for generations from farming or from the sea.
Split into simpler sentences: According to church records his parents were William Jamison (or "Jameson") and Mary Jamison (nee Fisher). For generations, his forebears had made their living from farming or from the sea.