Hanweir, the Writhing Township is one permanent represented by two cards. It behaves like any other creature does. It can attack and block. It has abilities that work. It can be enchanted or equipped. You can put counters on it. And so on. You can think of it as one big card while on the battlefield and you won't be wrong. It's one creature, so a single spell that says "Destroy target creature" takes out the whole permanent. If you're asked to sacrifice a permanent, you can sacrifice Hanweir, the Writhing Township.