Yes, yes they are. They fucking are brothers. Some problem with this?
You have a pair of EYES same as everyone and you can use them to read the tags and warnings that clearly say that it's INCEST, LIL BRO X BIG BRO.
And please don't come to us as the hypocrite one that mask himself as the pure, philanthropist guy/girl in the comments while still reading this. You're not better than us :)
What, do you perhaps really like this manga and to justify yourself for liking something "immoral" you feel better insulting us? ;)

they’re brothers..