In English peerage law, nobility / a peerage was held only by one man. It was inherited according to the rules of the specific peerage, but there was at most one heir. (It could go extinct, or some could go into abeyance for an indefinite time, depending on certain circumstances.) So for a living earl, neither his wife nor any of his descendents were in law noble as a result of that specific earldom ... though the only way you could tell after the Restoration of Charles II (when they abolished all other prerogatives and powers of peers) is that no other member of his family got a seat in the House of Lords, or trial by the Lords in case of a crime.

But that's about the law. Courtesy rank is rather a different question. There is a system of courtesy titles and styles, and it depends on rank and birth order. For earls specifically, the eldest son would likely use a subsidiary title of his father (viscounty or barony) if one were available. A younger son would be The Honorable Joe Bloggs or whatever, which is at least more than Mr. Joe Bloggs.

As for class standing: that is beyond my pay grade! I'm not even sure how one could answer the question.