How do you change a family member Apple ID password?

If you know the current password, you need to log into their Apple ID and then use the steps in the articles below.

 Apple ID Password Change.      

 What to do after you change your Apple ID or password - Apple Support     I suggest doing this before you change your

If they forgot the password.

For the Apple ID password, enter the Apple (iCloud) ID and click Forgot Password.

Apple ID - Manage            

Apple ID – Forgot Password