Our lock screen sign-in page keeps getting duplicate account pictures

We have multiple accounts on our home PC. My dad is the administrator, and my mom, and I are just a local account.

(Yes, when I installed a fresh Windows 10 OS, I ensured that the PC had no internet connection and only allowed for PC to log-in via offline account and not sign-in to Microsoft Account which would require Wi-Fi or ethernet connection).

For some odd reasons, on my local account (Doug), whenever I asked my dad (Fred) (aka the admin/host user) to sign into his Microsoft Account so that I can have access to our activated Microsoft apps account such as Word, Excel, etc. My local account picture gets duplicated onto his login account picture.

Now he likes to check his email a lot on Outlook – free personal email and calendar from Microsoft with the web version and not the desktop app. My sign-in account picture is now on his account picture whenever he sends or reply with a new email.

The problem: We keep getting a duplicated login account picture from time to time. Sometimes his login picture gets duplicated onto my account or my mom's and vice versa.

Solution that we want? We just want to be able to upload our own "local" login picture and not via outlook email account picture. I do not want to have to ask my dad to sign-in onto his activated Microsoft account and then all of a sudden, my picture gets duplicated onto his lock screen log-in account and then goes about to compose a new email and my lock screen log-in account shows up on his email account account. How do I prevent from this happening?

When he sends an email to another person, I fear that they will see my sign-in picture. I do not want that. We just want a local log-in account picture. Nothing more, nothing less. We just do not want to have any pictures on our outlook email account picture.

See picture below what the problem is.

Windows Version 21H1 (OS Build 19043.1110)