What are "Tzon Kodoshim"?
Rashi: They are [Korbanos] that come to Yerushalayim for the festival on Pesach.
Radak: It is like it explains "k'Tzon Yerushalayim b'Mo'adeha" ? Korbanos that Yisrael bring to Yerushalayim three times a year ? they are many.
Targum Yonasan: Like the Kadosh nation ? like the nation that becomes Tahor and comes to Yerushalayim on the Mo'ed of Pesach. Radak ? on Pesach there were great numbers of flock animals in Yerushalayim, for everyone brought his Korban Pesach 1 to slaughter it and eat it there, like the Torah said.
Malbim: All of them are an Olah 2 to Hashem. So all Yisrael will be Kadosh to their G-d.
Seemingly, there were not so many more on Pesach than on the other festivals. Every adult male must bring at least two Korbanos every Regel, and it is a Mitzvah to eat Korbanos every day of Sukos. Every Korban Pesach was a partnership of at least 10 people designated to eat from it (Eichah Rabah 1:2)! Perhaps many offered cattle on other Regalim; Pesach must be Tzon (a kid or lamb). (PF)
What is the source that they are Olos? Perhaps "Kodoshim" hints to Kodshei Kodoshim. (PF)
What are "Tzon Yerushalayim b'Mo'adeha"?
Refer to 36:38:1:1-3.
Malbim: They are Shelamim, to eat and rejoice in front of Hashem. So they will enjoy great good. 1
What is the source that they are Shelamim? Perhaps "Yerushalayim" hints to Kodoshim eaten in Yerushalayim. (PF)
Will destroyed cities be full of people?
Radak citing Targum Yonasan: The cities of the land of Yisrael, which were destroyed, they will be full of people of Beis Yisrael.