God is amazing in that He can have real people make real choices that have are rooted in metaphoric and spiritual meaning.
1.) It was the same people in that it was the nation of Israel who welcomed Him with much praise, and it was the same nation of Israel that demanded He be crucified. The thing to understand is that throughout all of their history Israel has been on a roller-coaster relationship with God. We see that in Exodus, Judges, Kings, all the prophets, and practically everywhere else in the Old testament. One generation praises God and is rewarded, the next generation loses it, gives in to idolatry and is punished. The amazing thing is that they do it over and over, the same mistakes time and time again. I would list references to exact passages but I'd take up the entire page with them. Here they simply were excited for God in that they thought this might be their "warrior king messiah" and when God's plan took a different direction they did what they do best. Turn away from God. Just like the Golden Calf in Exodus 32 and The idol worship detailed in Kings concerning the Prophet Elijah's constant battle with the false prophets of Baal.
2.) Understanding the biblical definition of "blindness" is key here as well. In John's Gospel chapter 12 it says,
37 But although He had done so many signs before them, they did not
believe in Him, 38 that the word of Isaiah the prophet might be
fulfilled, which he spoke: “Lord, who has believed our report? And to
whom has the arm of the Lord been revealed?” 39 Therefore they could
not believe, because Isaiah said again: 40 “He has blinded their eyes
and hardened their hearts, Lest they should see with their eyes,Lest
they should understand with their hearts and turn, So that I should
heal them.” 41 These things Isaiah said when he saw His glory and
spoke of Him.
Blindness was tool that God used over and over again to symbolize man's fallen nature. There was the messiah, God in the flesh right before them and they -could- -not- -see- -it! That was precisely the point though you see God's Will must and will always come to pass regardless of what scenario surrounds it. Just as the law required that the people of Israel sacrifice a lamb to God for the passover and for atonement for their sins. So to was the Messiah to be sacrificed. It had to be Israel who chose the death sentence despite Pilate's willingness to be merciful. If Jesus was never executed we the Gentiles would have no part in God's kingdom. We would not have Christ's remdemptive work to be our mediator to God.
3.) Israel was looking for a warrior king. Another David or something to that nature that would come and restore God's people to the position of power in the world. Their interpretation of scriptures called for that and they're still awaiting that today, which is why they, for the most part, will never accept Christ as the messiah until He returns. Fulfilling that prophecy just as the scriptures said he would. They were ignorant however that "The age of Grace" would come beforehand. How they missed Isaiah 53 & 54 I do not know but it's all pretty much detailed there if you need to reference. Chapter 53 detailing the messiah's life, death, and how they would not know who he was. Then immediately after that in Chapter 54 it details how the "barren woman" which is a depiction of the Gentile nations will now have part in the covenant. You see the flow there The messiah will come, then comes the age of the Gentiles, and God does this to create jealousy in people of Israel. All things work to bring people back to their creator.
Lastly, the reason I believe it was indeed the same people. Is because he was "sent to his own, and his own recieved him not." The people seen the miracles. Heard him speak. Were first hand eye witnesses, but still they turned away. Whether it was fear, or anger, or confusion doesn't matter. What matters is without them condemning him, without the blood, and cross. There would be no salvation.
I really hoped this helps you and If I'm in error I welcome any correction.