1)
Bearing in mind that the Torah already taught us 'Bein ha'Arbayim' in Parshas Bo, 12:6, why does the Torah insert the words "Bein ha'Arbayim be'Midbar Sinai"?
1.
Oznayim la'Torah (citing the Meshesh Chochmah): To teach us that 'Bein ha'Arbayim' is subject to the location where the Korban Pesach was being sacrificed, and not to the time that it fell in Egypt.