No they aren't, Jirou is Tarou's son tho his mum is unknown (he talks about his ex-wife so maybe its her)
and Miyauchi's dad is Kudou an some english man, and if im not wrong i read somewhere the he runs a school form butlers in England
ehmm.. i remember that Miyauchi's parents are both female (alpha female x female omega)
Alpha female is Jirou's mum.
**that alpha female is the same person as jirou's mum.
The English man is kudou's mum (his genre is male but also alpha)
**typo error.. idk why kept autocorrect..
**His gender is male
Jirou & Miyauchi are half-sibling, right?
since Jirou's mom & Miyauchi's parent is the same person.