Merging two flocks - looking for tips

I've heard to wait until they are all about the same age before putting them all together. I have gone about a week with just looking. I know a good way for them to be accepted is to wait until night time and put them all in the same sleeping area, you know when they all go into that sleep trance thing. I would put them all in the same sleeping area and then monitor the next day because the pecking order is going to have to be redone when they are merged. All of the chickens,even the ones that were together are going to start pecking each other in order to establish a new dominance. I would just watch them to make sure they don't get too aggressive and start plucking out feathers or anything.

I meant the same size, not the same age.

I would try the look but not touch thing for a bit and see when they start chilling out when they see each other. I've added I want to say maybe 2 month old chicks in with my older ones and it was okay as long as they can hold their own.

I would be careful, you have two roosters, merging/adding to roosters together is very hard and they will hurt each other, and the other hens...be careful.

General rule of thumb for adding younger birds is wait til at least 15 weeks old, they are pretty much as tall as they will get at that point. The roosters being that close in age may have some serious fights until dominance is established. Good luck

They may be close enough in size now.  I've often read recommendations to do the "look but not touch" thing for a month.  If it's already set up, you could give it a little more time.  if they are near the same height and don't seem like they want to get at each other through the fence now, it may go just fine.

They may get a little taller for another 4 weeks or so, and fill out after that, reaching adult weight and bulk around one year as an average.  It does vary with breed.

There's really no predicting how it will go, other than that they will have to find their new pecking order.  During free ranging and at night are in my mind two different approaches to mixing them.  If they free range all day without a real problem, there's no reason they can't share a coop that night.  Or, you could let them choose where they sleep, if your setup will allow it.  Often people set up a second feeder and waterer to minimize squabbles, and having hiding places available is a good idea, too, if you can manage it.

Good luck!

You could also put the larger birds in with smaller singly at 1 day intervals.  Work down pecking order using cockerel from elder batch first.  He should quickly secure highest rank in tractor but have too many targets to do real harm.  If not problems after 30 minutes, then repeat following day.  New dominant will suppress aggression by past flockmates as he asserts his dominance over subsequent introduced birds.