The fourth son Shosaku was adopted as a son of Yataro IWASAKI, the founder of Mitsubishi Zaibatsu at one year old, and was renamed Toyoya IWASAKI; he took active part in the business world as his real brother Seinosuke did.
四男・昌作は数え2歳で三菱財閥の創業者・岩崎弥太郎の養子となると同時に岩崎豊弥（いわさきとよや）と改名、実兄の誠之助同様実業界で活動した。