It either means
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Kim is an actor, as Q suggested, and this half nephew is MOS.
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Kim is MOS, and the half nephew is real deal good guy (Q disinfo or full of shit)
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Kim is an actor, the nephew isnt read in on the plan, and is about to get MOS'd or Q'd.
I'm going with 3, because I'm quite certain Q isnt full of shit, and Kim is an actor.