I think it’s a terrible clue.
Yes, obviously, ‘s can mean “is”. And obviously, kin is fine for people.
But it is very poor form for the “s” to be doing “double duty” - it is already performing the role of being “is”, so it shouldn’t also be doing something else, especially with no appropriate hint.
At best, it’s horrendously clumsy. No elegance to the clue at all.