If you have twins in your family add a Twin fact to each individual to designate the relationship.
Open your tree in Family Tree Builder. To add a fact to someone in your family tree click the Edit button on that person’s card. Then click Edit details (of person’s name) and go to the Facts tab.
Click ‘New fact’.
Select All Facts and then find Twin in the list on the right and click OK.
Enter the date, place and description if you have them and click OK to save.
Repeat for the other twin.