There is a chance he will be auto detected and banned, please have him contact a senior member of staff, (Administrator or above) and we can go through verifying that it is a separate person's account
Yes, he will be detected as an alt account and be permabanned. It's unlikely that you will be able to get him able to play on the server after you have been permabanned.
I think if your brother wants to play on the server you could try to message @Fredy or an administrator and they can verify that it would be your brother playing. But I am pretty sure your brother will get detected as an alt account.
There is a chance he will be auto detected and banned, please have him contact a senior member of staff, (Administrator or above) and we can go through verifying that it is a separate person's account
