expression, ichidan verb
speak unanimously; say the same thing
Used when multiple people say the same thing at the same time or express the same opinion. Often appears as 口を揃えて (adverbial form).
みんなが口を揃えて彼の提案に反対した。
Everyone unanimously opposed his proposal.
口を揃えて言う必要は
You don't have to all say the same thing.