I thought that was taboo to associate with anyone that was inactive
This is probably one of the biggest gray areas in WT world, (there aren't too many)
Mother says to constantly limit association, stay away, danger danger danger.
But JWs tire of hanging out with the same old people year after year. Their worldly, or faded family is often much more interesting, allowing them to "be themselves" for a few days without pressure of keeping up the JW act.
Good for your cousin, maybe the deacon will teach them a thing or two.