9 Close's relative's incident - law gets involved with it (9,4)
My answer is IDENTICAL TWIN... Which is the anagram product of mixing INCIDENT LAW IT, and it fits in with the cross word letters.
"Close relative" makes sense
But what about the first apostrophe... is that a typo?
Should it have been "Closest Relative's incident etc..."
I clearly have too much time on my hands..