Can't upgrade to two factor authentication because I'm in a family group

Every time I sign in to Apple I'm told my account has been locked, so I go through the rigmarole to unlock it.

Then I'm told to set up two-factor authentication, and start answering the questions, but I get to the point at which it asks me for the code for a credit card.

The thing is, it's not my credit card it's asking me about! My account is connected to my mum's partner's account as a family sharing member, and it's asking for his credit card details. Is it me, or is this massively insecure?

It also means that I can't set up two factor authentication for MY account.

Just to be clear, I am signing in with MY email address and password, but in order to turn on 2FA for MY account I'm being asked to provide details about the credit card of the person who pays for the apple TV+ subscription via a DIFFERENT account.