Kids bullying each other? Anger issues?

So I’m not the parent (older sister) so I don’t really know if I can post this here but I need advice for my two little brothers (8 & 10). Let’s call the younger J and the younger S.I don’t know if this is normal behavior or not since they’re boys but the bigger one bullies the smaller one a lot. He calls him names like stupid and fat (he’s just a little chubbier than him) and repeatedly makes him angry. Actually last night he said that and S was like no i’m not so he tried to prove himself and do a pull-up on our shower bar, which then lead to J trying to snitch on S, making S upset. When I tell J that calling others fat is rude, he tells me, “But it’s true!” and I tell him that it doesn’t matter because he shouldn’t be saying stuff like that in the first place. But he doesn’t listen to me. In fact, he loves to talk back and say “Okay and?” and “I’m older than him so I can do whatever I want” (When I say that I’m older than him and he should listen he says, “so?”) It leaves me frustrated as idk what to do in these situations.The back talk isn’t even limited to me; He does this to my mother and grandmother too. My father & grandma is away on a trip and my mom works all week so she gets stressed easily so she’ll try to just make both of them happy and make them not scream and yell (Which I suspect made them both a little spoiled) J will scream at my mother for trying to get him to eat a SINGULAR vegetable, screaming at her because she’s telling him that bullying S isn’t right, and even if she gets on his “nerves” and tells him to shower. Occasionally he’ll even say to my mom “Who do you think you are,” which BAFFLES me.As for the anger issues, because J loves to tease and bully S, S has gotten a habit of screaming and crying a lot (sometimes for the littlest things) as well as hitting the walls, thumping the floors and slamming our doors. Last week he kicked a hole into the wall. I’ve tried many times to calm him down and say that he’s destroying the house he lives in and that he’ll knock the whole house down if he continues and many times had him promise me he’ll try to stop but he never does. I don’t know if there’s someway to calm him down and to get him to stop and I don’t really know what to do with J’s rude behavior which causes S to have the anger issues.Sorry for the mobile formatting and/or this is lacking detail. via /r/Parenting http://bit.ly/2WaIACM