"Is three people enough for a class action, or does there have to be more?"
Depends on the rules of the applicable jurisdiction, but most are relatively similar to the Federal Rules of Civil Procedure, which require that "the class [be] so numerous that joinder of all members is impracticable." Fed. R. Civ. P., Rule 23(a). I can't conceive of a situation in which three parties could satisfy that requirement.
Nor can I imagine why three plaintiffs would want to go the class action route.
How could a county "handle" an estate matter?