As a sociologist I will try to give the point of view in sociology. And that is an interesting question, by the way.
When we use the word "society" in sociology, we designate a group of individuals who share norms, behaviors and a culture, AND who interact in cooperation to form a group or a community.
So what does it take to be consider as a society in sociology (characteristics)?:
1) It takes a group of individuals. 2) These individuals must share norms, behaviors and a culture. 3) These individuals must interact together in a cooperation to form a group or a community.
What means "norms" in sociology? - There are two types of norms in sociology:
1): The formal norms are the ones written in the law that every individual must respect.
2)`: There are the informal norms that are norms created by people in the society to regulate "how to behave" (some rules you respect in public). In other words, the informal norms are set rules to control the "way of behaving" in the society. You don't HAVE to respect the informal norms like you have to respect the formal norms.
What means "culture" in sociology? - Culture means "something that are common to a group of people and that fuse this group together".
That is why you can ONLY ACQUIRE a "cultural baggage", you cannot be born with culture.
Now I will try to respond to your question
Based on the definition of a society in sociology, can 3 people share norms, behaviors and a culture and interact in cooperation to form a group or a community? Yes.
Now, can these 3 people share norms, behaviors and a culture, interact in cooperation to form a group or a community AND AT THE SAME TIME be different from the rest (the people not included in their group of 3)? No.
Because these 3 people probably did not build their "own culture". Culture takes history and history takes time. Their culture must be coming from somewhere else, whether or not they want to admit it. They have ancestors, etc. 3 people can not have a total different culture from the rest of the world.
In other words, these 3 people, even though they are sharing norms, behaviors and a culture and interacting in cooperation to form a group or a community are probably similar to a bunch of other group of individuals not too far away from them. Which means these "bunch of other group of individuals" should also be included in the society.