Hi there. I have a little bro (only age 7) that has had some major unusual emotional issues lately. Let me count the ways:

-He has an extremely short temper. Whenever I or my family bother him he yells and screams in irritation.
-He is mostly angered by my younger sister, who is a bit older than him. She seems to constantly annoy him to the point of him exploding and shouting things like "I hate you!" They've never really gotten along too well.
-He pretty much gets angry and frustrated about every little thing. He complains about small things like his brand new shoes being too tight, or a pair of socks being too big. He's a huge sore loser when it comes to video games or any type of game.
-He constantly gets in trouble for pretty much anything and never learns to stop. My parents are the type that punish extremely harshly, and expect us to have good grades, not talk back, etc (I have social anxiety and depression mainly because of them). I feel extremely bad whenever my parents catch him screaming in anger, resulting in him getting grounded. But no matter how many times he gets grounded, he never learns.
-He lies way too much, and is terrible at it. One time, he broke a fancy cup (it wasn't glass) without anyone seeing, and attempted to hide it under a chair. Didn't end well.
-I try to teach him techniques like deep breathing, but he never seems to listen.

I don't know what the cause of these problems could be. He's never been bullied at school or had any sort of physical or mental trauma. What do I do?