1)
The verse implies that they slandered all the Jews. They slandered only Chananyah, Misha'el and Azaryah!
1.
Malbim: Chananyah, Misha'el and Azaryah did not bow due to Jewish law. The slanderers thought that the king will be angry at all the Jews, due to their creed, just like Haman was angry at all the Jews, for he found out that Mordechai did not bow to him due to his creed.
2)
What is the meaning of "Achalu Kartzeihon"?
1.
Rashi: They slandered the Jews. The Targum of "Lo Selech Rachil" is v'Lo Seichol Kortzin. I say that the custom was that slanderers were fed where they slandered. It was a sign to verify their words, Ibn Ezra ? one who covertly slanders, it is as if he eats his flesh.
