Pfftt! Yeah ,right! lol... I've been trying to merge my girls ...going on 2 weeks now. I tried " throw them all together at night when they are all sleeping, quarantine of course and then go about like normal."
The older sexlink hens are bullies. They run off the younger RIR, & won't let them near the food & scare them.
I have a system now. During the day I separate them..the young ones in the run/coop, the older ones free range in the open pen. Late afternoon I let the older ones out into the backyard to free range and then I open up the run for the young ones to free range the open pen. Even while I have all this separation going on, the young hens continue to hang out in the coop most of the day. Come dusk I open up the gates so they all go up and roost in the coop. I have been making them all roost together at night in the coop. At first there was a lot of squabbling. It's gotten better.
Next week I'm going to let them mingle during the day in the run & open pen. We tried to do this a couple times but I think the "look and don't touch" method is necessary until the young hens build their confidence. Reading this helped a lot.
MERGING AND ESTABLISHING A NEW FLOCK
http://www.bhwt.org.uk/cms/merging-and-establishing-a-new-flock/
In addition to all of this, I'm still trying to get the new hens to the point where they will let us handle them without them being stressed out. And here I thought owning chickens was going to be easy!