The family was as beautiful as it was complicated in most cases. For many, family included only those you were related to by blood. Sometimes to the degree of only including parents, siblings, and children. In other cases, the family included incredibly close friends and lovers.
In the case of the Astryd family, few people were part of it. Other than Desmond himself, only Claire Lynwood, Sashas Kor Ignis, Kyurustrae Exzar-Terra, Revna Von Mussel, and Cecilia Astryd formed this family. One big happy family that was somewhat odd for more reasons than just not sharing the last name.
The truth was that Desmond was the nucleus of the family; his love for the girls and the girls' love for him kept the family together. Yet, that wasn't enough; it couldn't be enough. For that reason, the girls had done their part to get along, to like each other, become friends and find what they could get along with, thus becoming a happy family.