Siri saved my reminder on the shared "family" list. How can I prevent this from happening again?
Settings → Reminders → Default List. This is where you can choose the list you wish to store reminders when you don't specify a location at the time of creating the reminder.


"Remind me to …" uses the list you select as the Default List in Settings.
"Add … to my … list" uses the list mentioned in that specific Siri command.