1)
Who were the Kohanim to whom the Pasuk is referring?
1.
Rashi (citing Zevachim 115b) and Rashbam: The Bechoros, who performed the Avodah until Aharon and his sons were chosen.
2.
Hadar Zekenim: The descendants of Aharon. 1
1
Refer to 19:22:151:1 . Torah Temimah, citing Zevachim 115b - It refers to Nadav and Avihu. See Torah Temimah, note 44.
2)
Why might the Kohanim think that they were permitted to ascend the mountain?
1.
Rashi: Because they come close to Hashem when they sacrifice Korbanos.
2.
Refer to 19:21:1:1.
3)
Seeing as, in Pasuk 24, the Torah writes "Pen Yifrotz Bam," why does it write here "Pen Yifrotz Bahem"? What is the significance of the extra 'Hey'?