No problems with the grid; relation of paired clues duly noted; I can find answers to 16a/17d which can be related to that "relation", but cannot see any connection to the only word that seems to fit in 26, which makes me think there is something else that fits into 26 that the standard word-finders are missing.
Also, is the theme "one hyphenated word", or "two words, one of which is hyphenated"? Any suitably oblique hints appreciated.