מְנַשֶּׁ֣ה אֶת־אֶפְרַ֗יִם וְאֶפְרַ֙יִם֙ אֶת־מְנַשֶּׁ֔ה יַחְדָּ֥ו הֵ֖מָּה עַל־יְהוּדָ֑ה בְּכָל־זֹאת֙ לֹא־שָׁ֣ב אַפּ֔וֹ וְע֖וֹד יָד֥וֹ נְטוּיָֽה׃ (ס)
Manasseh, Ephraim; and Ephraim, Manasseh; and they together are against Judah. For all this His anger is not turned away, But His hand is stretched out still.
Ibn Ezra on Isaiah
Manasseh, Ephraim, etc. This verse explains the preceding; Manasseh will fight against Ephraim, and both against Judah.
Rashi on Isaiah
and Ephraim with Manasseh With Manasseh, and together they will unite against Judah.