There is a description in "Gukansho" (Jottings of a Fool) (Vol. 5) with respect to the meaning of "the son-in-law of Yoshitsune" such that Imperial Regent FUJIWARA no Motozane states that "married a sister of Nobuyori to become a son-in-law" (Motozane married a sister of Nobuyori to become a son-in-law of Nobuyori), which could mean a husband of a sister was equal to a son-in-law; so "the son-in-law of Yoshitsune" is thought to have been a husband of Yoshitsune's sister.
「義経の聟」の意味については、『愚管抄』（巻五）に関白藤原基実が「信頼が妹に聟とられて有ければ」（基実は信頼の妹と結婚して信頼の聟となった）とあるように、妹の夫＝聟を意味する場合もあり、この場合「義経の聟」は妹聟であると考えられる。