God killed Jehoram's sons

In Elijah's letter to Jehoram, he said that God would smite his children and his wives with a great plague.

Behold, with a great plague will the LORD smite thy people, and thy children, and thy wives. 2 Chronicles 21.14

From that, I expected God to send a disease to kill Jehoram's wives, children, and people. But he sent some Arabians instead.

Moreover the LORD stirred up against Jehoram the spirit of the Philistines, and of the Arabians, that were near the Ethiopians: And they came up into Judah, and brake into it, and carried away all the substance that was found in the king's house, and his sons also, and his wives; so that there was never a son left him, save Jehoahaz, the youngest of his sons. 21.16-17

So I figured the Arabians just enslaved Jehoram's wives and sons (Elijah, God, and the Bible say nothing about the daughters). But then, the next chapter starts with this:

The inhabitants of Jerusalem made Ahaziah his youngest son king in his stead: for the band of men that came with the Arabians to the camp had slain all the eldest. 22.1

Which means that the Arabians didn't just take his sons and wives away; they killed them. And since God was the one who stirred them up in the first place, he deserves credit for killing Jehoram's sons. (The verse doesn't say what happened to the wives, daughters, or the rest of the people of Judah.)

How many sons were killed by the Arabians? The text doesn't say, so I'll guess 3.

God's next killing: Ahaziah (of Judah)