Hi:
May iIask why you want to move them, is someone sick?
Your 10gal tank will be a bit cramped, which may induce a little stress (which is what you don't want). You can add plastic decorations(I use PVC pipe cutouts)in this tank to providing hiding areas for the fish.
You can quarentine the small fish in the 10, But once you add three fish keep a watchful on the water paramters, 3 fish in this tank will quickly change the water quality. As far as the powder brown (I assume this is the sick fish-as these are known ich magnets), maybe place him in a seperate tank for quarentine.
The alternative of course is to place them in the 10gal, and keep and eye out for 3 things 1)-water quality issues in the q tank, 2)-fighting, and 3)- whether or not the disease to be treated is going away.
Is there a way of getting a rubbermaid 30gal tub, and using this as a q-tank instead? ($7bux at supertarget)
frank