thankQ uses the concept of a Household to represent a group of people that share the same Default Address.
The contacts do not have to have a relationship set up on the Relationships tab. Adding a contact to a household will allow you to make the relationship.
The household feature is most often used to group families together (e.g. Father, Mother, Son and Daughter) or Employers and Employees.
Once the household has been set up in thankQ you have the option to send only one copy of a mailing to each household group, rather than to each person in the household.