1)
Why did the B'nei Gad and Reuven, who said "Anachnu" in Pasuk 17, now say "Nachnu" minus the 'Alef'?
1.
Oznayim la'Torah: When they thought that all the men would cross to fight, they said "Anachnu", but now that were they told that only the seasoned troops would go, 1 they said "Nachnu". 2
2
Oznayim la'Torah: In similar vein, when, in Mikeitz Bereishis, 42:11, the brothers were telling Yosef about their family, they said "Kulanu B'nei Ish Echad Nachnu", because Yosef was missing; and Moshe, in his humility, said to the people "ve'Nachnu Mah".
2)
Why did the B'nei Gad and Reuven change the conditions that Moshe arranged in Pasuk 30?