"It's not rocket science."
That's the laziest shit I've ever heard and nothing more than an excuse.
They don't need to punish anyone for sharing a computer - and it's not that difficult to handle a situation like this. Currently, neither of them have done anything malicious nor have they committed a punishable offense. If they do, only then should both accounts be banned - whether or not it was the bigger or little brother, that hardware ID should be banned and since both share that hardware ID - both know the risks.
However, NEITHER of them are doing anything fucking wrong.
ESEA is just lazy, and a shitty company. It isn't rocket science to understand they're shitty.