They's not straight with trio summoned by old king (8)
I believe the answer is:
fiddlers
'they's' is the definition.
Both the definition and answer are plural nouns.
Maybe they are linked in a way I don't understand?
'not straight with trio summoned by old king' is the wordplay.
I cannot quite understand how this works, but
'king' could be 'er' (abbreviation for Edward Rex, various English kings) and 'er' is present in the answer.
This explanation may well be incorrect...
(Other definitions for fiddlers that I've seen before include "Tinkerers or violinists" , "Old King Cole's trio" .)