Regardless of it it had been your younger sibling or yourself, these actions were done using your account.
Here is Zazz's chest nice and full:
And here is where you placed rails underneath...
It is assumed that at this point a minecart and chest were placed underneath, sucking the items out of the chest.
If this was in fact your brother he'd better run, because you have 7 days free to kick his butt as it stands right now...