When I read your question, I thought you might not be aware that Japanese doesn't even have a plural form in the first place. However, looking at your past questions, you do seem to know the basics of Japanese grammar, right? Many languages, including Japanese, don't have dual or even plural forms, but of course, you can still count numbers or say "both of the two", "either of us", etc. Conversely, English doesn't have honorific forms of verbs, but that doesn't mean you can't speak respectfully in English. From this answer:
every language can sufficiently convey any idea that can be expressed in another language. The difference is that for each language there are some properties that must be specified when an idea is conveyed, even though they may be entirely optional in another language.
Here are some Japanese ways to say both, either and each. Refer to any online textbook for details.