מְנַשֶּׁ֣ה אֶת־אֶפְרַ֗יִם וְאֶפְרַ֙יִם֙ אֶת־מְנַשֶּׁ֔ה יַחְדָּ֥ו הֵ֖מָּה עַל־יְהוּדָ֑ה בְּכָל־זֹאת֙ לֹא־שָׁ֣ב אַפּ֔וֹ וְע֖וֹד יָד֥וֹ נְטוּיָֽה׃ (ס)
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.