1)
What is the meaning of "Mechalelim b'Chalilim"?
1.
Rashi, Radak: They played flutes.
2)
Did the land truly cleave?!
1.
Rashi (from Tamid 29a): The Nevi'im exaggerated, just like people speak. Radak - this shows how great was the Simchah. Also the Torah exaggerates - "u'Vetzuros ba'Shamayim" (Devarim 9:1).