Left: Actually, to me "King Arthur" is Graham Chapman, but he wouldn't have fit the tone of the story.
Right: Gwenhwyfar ferch Ogrfan Gawr
Drwg yn fechan, gwaeth yn fawr.
"Gwenhwyfar, daughter of Ogrfan Gawr,
Bad when little, worse when great."
If my Arthur looks familiar to you, you probably need no explanation about whom Guinevere's design is cribbed from.
On the top right is Oisc of Kent (some detail seems to have been lost in the process of adjusting scanner settings) and on the bottom, Meleagant or Melwas.
As for Guinevere, too eager to please her family and friends, and thinking things would work out for the best, she agreed to marry a man who's madly in love with her but whom she only likes as a friend. The temptation when she met someone for whom she did feel true passion, and the guilt accompanying it... her position is extremely unenviable.
Right: Arthur sometime between Kay's death and Camlann. It would have been by design that he doesn't grow up so much as wear out, becoming gaunt and empty-eyed in his 20s.
Left: Long before she was Arthur's creepy half-sister, she was the benevolent but distant queen of Avalon. Standard modern elf design mixed with a soupçon of Maleficent (the only character or element I liked about Sleeping Beauty).