Will Hashem literally call to them?
Radak: It is as if He calls to them. He will put in their hearts to come.
Malbim: This is a parable. It is as if Hashem has a quarrel with and a case against Yisrael for sinning against Him, and He calls the Mishpechos and Mamlachos to be judges between them.
What are "Mishpechos Mamlachos Tzafonah"?
Radak: Mishpechos refers to the nations, and Mamlachos are the kings - the heads of the kingdoms. Due to the kings (Melachim), they are called Mamlachos. The verse refers to the kings of Bavel; the greatest was Nebuchadnetzar. It says about them "v'Nasnu Ish Kis'o", i.e. when they will besiege Yerushalayim - "v'Nargel Sar Etzer Rav Mag v'Chol Rabei Melech Bavel" (39:13).
Why will they put their thrones at the opening of the gates of Yerushalayim?
Malbim: They are like judges who sit on the throne of judgment to hear the litigants' claims. They will sit also on the walls, and in all cities of Yehudah, as if they are divided into many Batei Dinim, a Great Sanhedrin and a small Sanhedrin.
