Ch. 1+2 blood related brothers, though they certainly don't look like it
Blood related brothers
Vol.3 Ch. 1.5 (Twins)
3. couple (stepfather&son)
Pg1-16 (stepbrothers)
father & son (non-con) & cousin (?)
Trauma-traditions creeping forth (father had been assaulted by his father and fights the urge to treat his son the same way)
Father & son (seriously fu##ed up in every sense of the word)
Blood-related brothers (how? totally different o0)
Mayonaka no Oyatsu