1)
Why does it say "v'Chohaneha Albish Yesha"?
1.
Radak, Malbim: Since they wear Bigdei Kehunah for Me ("Kohanecha Yilbeshu Tzedek" - 9), I will clothe them with clothes of salvation.
2)
Verse 9 said that the Chasidim "Yeranenu". Why does it say here "Ranenu Yeranenu"?
1.
Radak: Since the Leviyim sing for My sake, I will influence that they sing amidst Tov Lev.
2.
Malbim: They will sing amidst great Simchah.