Any way to get an unwanted person out of your Apple ID?

Ok I don't think there's a way to do this but I ll ask any way. So my girlfriend s family is super nosy and she s not supposed to be dating me. She got a notification that said her brother had joined her Apple ID or whatever. I was wondering if there was a way to boot him off of it. Another problem is that she doesn't even know the password to her Apple ID. Since they re so nosy, they had her other brother set up the account and keep the information. I think the only solution to this problem will be to create another Apple ID to use on an old iPhone that I have. This way the information will all be with me.

Change your Apple ID password and enable 2 step verification.

Changing the password to one only you know should boot them off the account with no way of signing back in.

Enabling two step verification adds another layer of security to your account. Any time a new device tries to sign in with your Apple ID, they need to also have a code that is sent to trusted devices that you select. So even if they find out your new password, they won't be able to sign in without the code that is delivered to you.