1 Heb “Say to.…” The imperative אִמְרוּ (’imru, Qal imperative masculine plural) functions rhetorically, as an example of erotesis of one verbal form (imperative) for another (indicative). The imperative is used as a rhetorical device to emphasize the certainty of a future action.
2 The suffixes on the nouns אֲחֵיכֶם (’akhekhem, “your brother”) and אֲחוֹתֵיכֶם (’akhotekhem, “your sister”) are both plural forms. The brother/sister imagery is being applied to Israel and Judah collectively.

In other versions

Say to your brothers, “You are my people,” and to your sisters, “You have received mercy.”

“Say of your brothers, ‘My people,’ and of your sisters, ‘My loved one.’

Call your brothers: My People

and your sisters: Compassion.

“In that day you will call your brothers Ammi—‘My people.’ And you will call your sisters Ruhamah—‘The ones I love.’

Say to your brother, “Ammi,”

and to your sister, “Ruhamah.”

Say ye unto your brethren, Ammi;

And to your sisters, Ru-hamah.

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