"Akkun and Onii-chan" pg 114-145
blood-related brothers
Father abuses son
stepbrothers
stepbrothers
Ch. 5 though..well.. all pretty well-behaved. Step-siblings with a weird monopolistic battle going (all three of them)
Hard to explain without giving every plot-twist away - but whatever it is, it's not blood-related.
Half-brothers
Somehow...the whole family
uncle & nephew (beware: dropped, so forever unfinished)
Ch. 2 Stepbrothers
Wana Wana Kiss