I need help creating an Archer and a Rogue with CR 9 each

[Vox Silentii]

Title says it all.
But im creating an encounter where they meet an old adventuring group and there is no CR 9 for those two.
I'm using
Champion for the Fighter
Evoker for the Wizard
Warpriest for the Cleric

I was thinking of using the Archer and the Master Thief but im having trouble scaling them.

[JackPhoenix]

Assassin is CR 8, that's close enough. Flind is CR 9, and can serve as a good base for archer NPC. Or take another champion, give him a longbow, and switch the stats around a bit.

[MaxWilson]

Title says it all.
But im creating an encounter where they meet an old adventuring group and there is no CR 9 for those two.
I'm using
Champion for the Fighter
Evoker for the Wizard
Warpriest for the Cleric

I was thinking of using the Archer and the Master Thief but im having trouble scaling them.

Just make a level 12ish Thief and a level 12ish Arcane Archer. CR tends to be pretty close to character level but typically a little lower.

Honestly you're better off ditching CR for this scenario entirely and using PHB rules for all the NPCs. You'll have a better feel for how they stack up against the PCs that way.