Is he really his brother?
theoretically, yes.
the brain took over noritoshi kamo and impregnated that woman 9 times which resulted in choso and his brothers being born
then it also took over yuji's mom
now im not sure if yuji was born before or after the brain controlled his mother but we'll see more later on
tho its entirely possible they are distantly related, since during yuji and choso's fight, choso saw visions of yuji and his brothers and thats why choso feels like a big brother towards yuji
Ok got it
choso big brother ;(