In the common app they ask if any family members attend but is there anywhere I can add info about a family member who worked there?
Unless the family member is a current employee it is totally irrelevant.
Again, unless that family member is your parent, it really is not going to do anything to help your cause. Even then, your application will still have to stand on its own merits for admission (you might get a bump if your parent is on the faculty or a high ranking administrator at the school). Otherwise, parents would just have the perk of tuition benefits.
^^^ current staff here - faculty, staff, and their spouses/partners can receive a benefit if they attend classes at Dartmouth but there’s no tuition benefit for children of Dartmouth faculty or staff.