1) Lots of people THREATEN lawsuits. Until one is filed and you are served, I wouldn't sweat it. But you obviously already are.
2) Lawsuits can be filed, but can still be without merit. But you obviously knew that.
3) Sounds like it is without merit, but if one is filed get a lawyer anyway. And countersue them for malicious and frivilous suits. Because it sounds like they don't have a leg to stand on.