Mitrophan's surname is not Yang, it's Chang. Yang is part of the given name Yangji. He was survived by his son Fr Sergei Chang during the Boxer Rebellion.
In some earlier accounts, renders his name as Tsi-Chung, which was a transposed transliteration of the surname and last character of the given name Цзи Чун from early Russian accounts, published in the Great Horologion by the Holy Transfiguration Monastery, Brookline, MA
Apostoliki Diakonia in their Greek Synaxarion of the Chinese Martyrs renders his name as Αγιος Μητροφανης Τσι-σουνγκ which translates to St Metrophanes Chi-Sung.