Birthday reminders are sent to second cousins (and closer) of the person with the birthday- both seven days before the birthday and on the day of the birthday itself. The reminder includes a link to add a special birthday greeting which will be delivered to the person’s profile on their birthday.
A family member may decline to send birthday reminders from within their profile page (or any of those which they manage). If they would not like to have birthday reminders sent on their behalf (or any those profile which they manage), you may simply uncheck the ‘Send Birthday Reminders to ...family’ checkbox within the Basics section of the said profile. One may also turn off this option for any profiles you can edit.
* Note: Please keep in mind that you will not receive birthday reminders regarding your own birthday.