Your parents are enabling his addiction. Its like a drug dealer and a drug addict relationship. There is absolutely nothing you can do unless they stop feeding his addiction to begin with and thats just the start. They have to take control of the situation. Take the games away, regulate his playtime. There is also no excuse for any parent to accept their child not going to school. It sounds like you are the one person in the family that is really seeing what is going on.

I kick my little brothers' asses all the time. It is my sworn duty as an older brother.

If it was me in this situationI would take away the consoles and games from him.

btw when I say kick his ass ... I dont "literally" mean his ass.

Anyone with a little brother(s) knows what 'kick his ass' means in this context.

That's a pretty delicate situation. Clearly you care for your brother and for your family too, but talking sense into him is the best thing you can do at this moment. Since I don't know how dynamic are things between you and him, I wouldn't suggest using force to kick his addiction as I can't foretell his reaction. Also, overlooking his first purchases of 500 bucks was a bad idea. Although unintentionally, his behavior got reinforced. 

And there could be a whole different aspect to it. He is in his teens. Addiction to gaming is expected. And so are troubles in school. It could also be possible that he is avoiding school for reasons not yet known to you. Teen troubles, bullies, girls. Could be anything. I would watch out for indications. Depression, reclusion, keeping to himself, short-temperedness, ignoring his friends. Do his friends come over to meet him or check him what is he up to? If they are, you can ask them about the school. If nobody comes-- now that spells trouble.... 

Ya well said lol, btw what Xxain said was very good as well.

My mom would have whopped me so hard.

Your parents seriously need to get their priorities straight. Still buying him games? Thats terrible. Worse than all the rest (cept Maybe the stealing)

Kick his ass? Seriously he needs to be dealt with force (i don't mean physical)