Final answer:
The least likely type of family group to continue existing is the moiety, which is a social division of a society into two groups that only allow marriage between individuals from different moieties.
Step-by-step explanation:
The type of family group that is least likely to continue existing is the moiety. A moiety is a social division of a society into two mutually exclusive and collectively exhaustive groups. Each moiety is typically exogamous, meaning that marriage is only allowed between individuals from different moieties. This can lead to a decrease in the number of individuals within each moiety over time, making it less likely for the moiety to continue existing.