Another way of reading his last name was 'Yamanami,' but he signed his name as '三南 (Sannan)' and '三男 (Sannan),' so it was highly likely that his last name was pronounced 'Sannan.'
読みについては「やまなみ」という読みがあるが、本人の署名に「三南」「三男」などがあるため、さんなんの可能性のほうが高い。