Let's be honest, introducing new chickens to an established flock is less "welcome to the family" and more "feathered thunderdome." MarionberryTop1472, you are not alone in this chaos. The pecking order is real, and it's ruthless. Your two new pullets (a Wyandotte and a Plymouth Rock) are currently living in a chicken tractor while your mature Easter Egger and Brahma hiss and lunge like they're defending the last meal on earth. And then there's the wild guinea, who might be male, might be female, and definitely thinks he's the head of security. It's a lot.
Here's the thing: your older hens aren't necessarily "distressed" in the way we humans think of it. They're annoyed. They're territorial. They're saying, "Who are these strangers, and why are they in my yard?" That rancorous behavior, the lunging, the pecking, the general fowl play, is their way of establishing who's boss. It's not personal, even when it feels personal. The good news is that your approach of keeping the pullets separated but visible is actually solid. They need to see each other, hear each other, and slowly accept that these new featherballs aren't going anywhere. The chicken tractor in the run is a great move, it lets everyone size each other up without bloodshed.
But let's talk about comfort for your older hens. They're not going to feel better because you give them extra scratches or talk to them in a soothing voice (though you should still do that, because you're a good chicken parent). What they need is time and a clear signal that their resources, food, water, roosting spots, are still theirs. Make sure you're feeding the older girls first, before the pullets get their turn. Give them a little extra treat, like a handful of mealworms, in their usual spot. It sounds small, but it reinforces that they're still top of the pecking order. Bullying usually escalates when the established hens feel threatened, not when they feel secure.
As for preventing bullying long-term, the slow introduction method is your best bet. Keep the pullets in that tractor for at least a week, maybe two. Let them free-range together only under supervision, and be ready to step in if the older hens gang up. If you see one hen getting cornered, break it up with a broom or a spray of water, but don't punish the aggressors. They're just being chickens. Eventually, the pullets will learn the social rules, and the older hens will accept that these new birds are part of the flock. It might take a few weeks of squawking and posturing, but one day you'll look out and see all four of them scratching for bugs together. Until then, keep the tractor close, the treats handy, and your sense of humor closer.