1)
What exactly, did all Yisrael do?
1.
Ramban (to 12:43): They circumcised themselves and their slaves before bringing the Korban Pesach.
2)
It should go without saying that the Bnei Yisrael did as Hashem commanded!
1.
Maharal (Gevuros Hashem Ch. 38, p. 142): The Bnei Yisrael needed the merit of Korban Pesach in order to be redeemed -- and the prerequisite for the Korban was to perform Bris Milah. Our Pasuk tells us that every male among Bnei Yisrael was in fact able to undergo the Milah; not even one person was held back due to illness, or by his brothers having died from the Milah.
