If the three criteria to become a family are shared finances, shared accommodation, and sexual relations, a group of students sharing accommodation could meet all the criteria. If they are engaging in sexual relations with each other, are sharing the payment of bills, and living under one roof, they would meet the criteria for a family group. Does this mean they can be considered a family for sociological purposes?
Additionally, when children grow up and leave home, they are no longer be living under a shared roof as their siblings and parents, but few would say they stop being a family. Therefore, a shared residence should not be a critical component of a family.