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:
(https://www.opticraft.net/proxy.php?request=http%3A%2F%2Fi.imgur.com%2F2FAQv4z.png&hash=f40055451c4386d158d7a393f4f0374e)
And here is where you placed rails underneath...
(https://www.opticraft.net/proxy.php?request=http%3A%2F%2Fi.imgur.com%2FFE1SGSq.png&hash=c7d9515c9436d96466761769ba906256)
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...