You dumbass fucking gorilla no he's suspicious why his brother is alive, he's not looking for excuses. What if the uncle did something to his insides? Maybe that's why he's suspicious.
Edit: I wrote this when I was really angry at something else.
Both does have a valid argument here.
Yeah killing people is obviously not an morally OK thing to do in most worlds.
And if the uncle got away without punishment it would be pretty questionable.
But the reason for his betrayal and why he spared the brother is a valid reason to seek him out too.
Revenge is not going to make it better anyway and the answer could help prevent future tragedies too.
I mean i think uncle was clearly insane at that point and the only borderline sane thing he has is his twisted(?) fatherly(?) love to his nephew. Him actually killing his other older nephew would probably break MC frfr so thats why he spared MCs brother, atleast thats what i think