I'm guessing all of your family members are using the newest version of teamviewer 12? If not, you should try and update if possible.
Also, everyone of you has to set their own personal password. To me it looks like only you and your sister created a password and your brother did not.
What happens if you type in the Teamviewer ID from your brother?
Does the "enter password" windows pop up or nothing happens? If the window pops up and it says "wrong password", maybe your brother should try and change his password and then try again.
I answer and explain:
- As far as I know, they all have version 12
- Me, brother and sister set up the same personal password for unattended access
- I and my brother tried to reconfigure the personal password ... (works as it wants, ie today we set up, works a few hours, but the next day I have refused to authorize and request a one-time password) - brother does not have a problem with it
- My brother added my ID to the "manage additional passwords" list and also set our common password
- When I click on the brother's computer icon (ID) in the list of computers / contacts, it is trying to connect, but ends with a password prompt (same as selecting "connect remotely with password").