They both sound wrong, don't they. I think it should be plural - they're each gripping - but it sounds wrong. And what are they gripping on to? (I know it may be clear from elsewhere) One option would be to re-cast the sentence.
Should the narrator, if his/her perspective is not that of the age being written about, use that kind of distinction in descriptions?
It's a very nice question - one of voice as much as anything. Probably the narrator needn't, but we'd need to know how the other characters saw them. It's frightening how recently a person's class seemed as integral to their nature as their gender still does, and only slightly more mutable.