Ratboy Genius is actually Little King John's ancestor.Ratboy is either one of Little King John's grandparents (great or otherwise) or a parent, with Little Summer Solstice Baby being the grandmother or mother. It would explain Little King John's near resemblance to Ratboy if he was a hybrid, Ratyboy's own slight stretching capabilities, and Little King John's obsession with the Little Summer Solstice Baby.
Little King John is Ratboy Genius' evil side.They're both ratboys, both kings, both build things, both love the Little Summer Sostice Baby... And at the end of one of the videos, Ratboy's hand stretches in a similar fashion to Little King Jonhn's as he contemplates the villain...
Ratboy Genius is a Reality Warper.Ratboy's Kingdom is actually a pocket dimension created by the Ratboy Genius. It exists outside of our world, and he can freely come and go, hence why Ratboy can go to space, the beach, the Whitehouse, etc. and why he can change the way his world looks, and his and other characters' models and voices, as well as why all the other characters hold him in such high esteem. He's basically the god of their world, and is responsible for every part of their existence. When he's not playing with them he comes to our world to terrify its denizens.
Little King John is not a rat, but a Wicked WeaselThis explains the stretchy neck, and why his ears are shaped differently from Ratboy's. It even explains why he loves taking things from other people◊!