Ben is brother to Pat;
Daisy is sister to Tori;
Gail has two big brothers: Carl and Kyle, who look very similar.

They all stay close to town, don't like to venture out. But then there's the other side of the family...

Joe has a brother called Sean;
Vince has a sister called Fannie;
Zoe is sister to Sam. 

These folks still live in town but also travel further up, where the air flows more freely (so they say). 

It's an odd family, you'll see them out and about in couples but they never leave or come home with each other. I can tell you more about them (new hints every 24h), but maybe you already know what I'm talking about.

What links these sets of siblings and what divides the two groups?