yeah, if you remember your account names and passwords, install etqw, then go to activate existing online account and use those account name(s) & passwords.
if you don’t remember your account names, ask brother to launch game, log off his account in game, then go to something like “check all account names associated with this DVD-key” - this will remind you your forgotten account name(s) (but it won’t tell you the DVD-key of course).
I am not sure but alternatively you could perhaps just copy the whole etqw installation folder of brother to your pc instead of installing it new. should work too. But of course it will not allow you to create a new account without DVD-key - you will only be able to reactivate your old ones if they still exist. But in any way a clean install since you got the DVD will be probably better.