1)
Why did Daniel tell Chananyah, Misha'el and Azaryah?
1.
Malbim (17): Also they will isolate themselves. Perhaps there will be Ru'ach [ha'Kodesh] on them, according to their preparation.
2.
Malbim (18): Also they will pray for mercy. The Tefilah of four is greater than the Tefilah of one!


