Statue of Alan Stewart (left) and the fictional David Balfour (right), from Robert Louis Stevenson's Kidnapped.

Is this the only double statue that features a real-life character and a fictional character?

THE AUTHOR ROBERT LOUIS STEVENSON was born in Edinburgh in 1850. He based many of the characters and circumstances in his 1886 adventurous tale Kidnapped on actual people and places. Two such individuals were David Balfour and Alan Breck Stewart. At the conclusion of the story, the two characters bid farewell to one another at a spot referred to as “Rest and Be Thankful” on nearby Corstorphine Hill. This might explain their unusual placement on a busy road on the outskirts of Edinburgh’s city center. The statue was designed by Scottish artist Sandy Stoddart. It was unveiled by Sir Sean Connery, another of the city’s legendary citizens, in 2004. The grounds adjacent to the monument once boasted the Balfour Stewart House, the headquarters of a brewing company that was demolished in 2008. Quoted from Atlas Obscura

The main character and narrator [in Kidnapped] is 17-year-old David Balfour. (Balfour is Stevenson's mother's maiden name.) His parents have recently died, and he is out to make his way in the world. He is given a letter by the minister of Essendean, Mr. Campbell, to be delivered to the House of Shaws in Cramond, where David's uncle, Ebenezer Balfour, lives. Quoted from Wikipedia

The statue, depicting characters from the Robert Louis Stevenson novel 'Kidnapped', sits facing Western Corner, an important site within the novel. Quoted from the Canmore website

Alan Breck Stewart was a Scottish soldier and Jacobite. He was also a central figure in a murder case that inspired novels by Sir Walter Scott and Robert Louis Stevenson. Quoted from Wikipedia