Those are John and Joe! Mono's dad and uncle!

Nope, their names are not "Bird Joe" and "Bird John", people call them Bird Brothers because most of the population on Mono's city are mammals. There are few birds, fewer related birds... So yeah, the name stuck.

John was actually the younger brother, but he was always the most assertive and loud of the pair, so people assumed he was the oldest.

They were kinda of... Street fighters of sorts. They couldn't fly, but since not everyone knew that, they used their feather light bodys in their advantage and were pretty strong on the fighting niche. Lots of broken bones, tho... Since they are birds and all...

They distanced themselves from each other after John started getting in fights to protect prostitutes and oppened his own strip club with the girls he protected. Joe just kinda of felt uncomfortable around too many girls and didn't like administrative work... Or stripping for people... So he went to the other side of the city and became a helper at a bar... Their work schedules and interests became gradually a wall between them and they just talked through letters, if ever...

John started to mail Joe more often talking about a certain kitten he wanted to adopt before he died