Can someone explain what the wedding is about? I am extremely confused who Iori married.

that black haired lady. not the light haired girl

he married the light haired aunt Hisayo, who is the heir of the wealthy Yonkura family. the dark haired lady is his mom. I always thought that there was something between his mom and Hisayo (chp.2). I thought she married Iori to be near his mom (and maybe to have a kid it seems).