1)
Why does it mention "Beis Yisrael"?
1.
Radak: You did not trust in them - bless Hashem, for He saved you from those who serve idols!
2.
Malbim: Above, it mentioned praise - "Hallelu Ovdei Hashem" (1). Now it adds that Beis Yisrael should bless Him. I.e. via their deeds they will open a source above to influence Brachah on them, like I explained above (refer to 134:1:2:2).
2)
Who are "Beis Aharon"?
1.
Radak: They are the Kohanim who serve Hashem.
