The true story of Cowboy Charlie Siringo is one of adventure and hardship on the Texas range. He faced many challenges but persevered with his cowboy spirit.
Since I'm not familiar with specific Bob Barnard and Bob Armstrong fanfic, it's difficult to say. But common themes in fanfic in general can include friendship, adventure, and overcoming challenges.
Uncle Bob in the 'We Kids Uncle Bob Stories' is likely a character who has a special relationship with the kids. He could be a family member, like an actual uncle, who enjoys sharing his experiences and stories with the younger ones.
Bob Wills was likely a very important figure. Maybe he was a musician or an artist of some sort. Since he's called the 'king' in the story, he must have been highly respected in his community or field.