Are there words that are plurals for plurals?

For example, 'sheep' and 'fish' (though 'fishes' can also be used as a plural form).

The pronoun-verb combination 'you are' is the singular or plural form; for example: Jane, you are next.Joe and Jane, you are next.Boys and girls, you are next.

Most mass nouns (non-countable) nouns have no plural forms, e.g.:data (this has now replaced datum as the singular form), information, suspense, air, any of the elements

Plural is more than one. Example: tree = trees ( there's more than one tree)

were e.g. I was but they were