Which descendants of Chizkiyah will serve in Melech Bavel's palace?
Rashi (from Sanhedrin 93b): Chananyah, Misha'el and Azaryah.
Radak (Melachim II, 20:18, from Pirkei d'R. Eliezer 52): Daniel, Chananyah, Misha'el and Azaryah. We find that they were in Melech Bavel's palace, and they were from Yehudah, and Nebuchadnetzar asked to take descendants of the kingship and the nobles (Daniel 1:3-6).
What is the meaning of "Serisim"?
Radak (Melachim II, 20:18 citing Sanhedrin 93b #1: It is literal (they were castrated).
Radak (Melachim II, 20:18 citing Sanhedrin 93b #2: Idolatry was castrated in their days (all recognized that it is impotent).
Radak (Melachim II, 20:18, citing Targum Yonasan): They were officers.