1)
Why does it mention Bnei Yisrael and Bnei Yehudah separately?
1.
Radak: First Bnei Yisrael began to anger Me, and afterwards Bnei Yehudah.
2.
Malbim: The verse equates them; both did evil from their youth, i.e. due to habit from youth.
2)
Why does it say "Ach"?
1.
Radak: This affirms the matter, like "Ach Atzmi u'Vesari Atah" (Bereishis 29:14), "Ach la'Sheker Shamarti" (Shmuel I, 25:21) and similar verses.
3)
What is "mi'Ne'uroseihem"?
1.
Radak: It is from their youth, i.e. the days in the Midbar, like I explained (2:2).
2.
Malbim: Refer to 32:30:1:2
4)
Why does the verse repeat "Bnei Yisrael"?
1.
Rashi: The 10 tribes did worse - they acted in order to anger Me.