I don't understand how quisque and quique are different. How can a pronoun referring to all people be singular or plural? In which situations would one use either of these?
Latin does indeed think about number slightly different than we do in English--or Latin reflects subtleties of reference in a slightly different way. Quisque is the indefinite pronoun, masculine nominative singular. Quique is the indefinite pronoun, masculine nominative plural. Quisque clearly means "every [single] one" or "each one." Quique has the same meaning, but distributed across a group: "every [single] one [of this group]," or "each one [of this group]." Does that make sense?