It would be easier to have them separate, but you need to consider the birds. Are they bonded with each other? Separating bonding birds is not a good thing to do, and you need to make sure they aren't bonded. It is likely than they are bonded, but there are ways to tell.
Bonded birds will preen each other, feed each other, kiss each other. Bonded birds also sit together a lot and keep each other company, they will probably eat at the same time together and preen at the same time as well.
They probably all wouldn't want to be separated; they are flockmates, and separating them would be tramatic. It probably would be best not to separate them, bonded well or bonded little.
My advice to you is just continue what you're doing. Work with them all equally, but don't rush the two who aren't cooperating. Go at their pace. If they don't want the big scary hand and perch near them, then don't put it near them.
