This is how my son great up - we had a bunch of kids in the neighborhood and the deal was that they were either at one of the 5 houses/yards or in an obvious place like the cul-de-sac on their bikes and roller blades. We all knew each other and had a generally good feeling about supervision. We left the kids alone. We did not supervise their discussions, arguments or decisions on "ring leading". If someone got his nose out of joint or got tired, he came home.
Of course you want to protect your kids. But that's not how life works. I know you don't like to see harshness - in fact, you're so worried about it that you even posted that you don't want answers that are harsh to you. I think you may be an extremely sensitive person? Do you get hurt easily? Did you grow up this way? Is that what you fear for your kids? I do feel badly for you if that has been your experience.
How is it that you think kids learn if they don't experience things? They are all experimenting with leadership (you call the other kids "ringleaders" but call your daughter "bossy") - so you know they are playing this same role at different times. Some kids are leaders, some are followers, some vacillate in between while they are learning and working it out. They're going to make mistakes in school, and that's why they practice with homework, right? To get things right over time? Well, friends and relationships are the same way.
But that's different from someone showing up when your daughter has a friend over - no, they don't just barge in and take over. You tell them that Mary has company and she'll play with the neighborhood kids another time.
I also think that kids gauge a lot by their parents' reactions to things. If WE don't get so upset and if we don't watch them every second of the day, then they have to learn, observe, adapt and react on their own. That's very different from keeping them safe overall - but running around the neighborhood in a group is really wonderful life experience.
You cannot micromanage children's relationships. If they are upset, you help them figure out what THEY want to do. You help them figure out what to say, when to come home, when to break from the group. You cannot, should not, and must not get so involved that you are getting hurt on behalf of children doing normal kid things. Your instant reaction to the donut thing is that her mother got involved and told the kids not to play with your daughters? I think it's a huge stretch to think that this mother is also so over-involved that she is dictating what her kids do with respect to yours.
Around here, we tell the kids to work it out, and if there's an argument, to say "sorry" and move on, to get out the bikes and the skateboards and the kickball and start a game.
I think you will be much happier as a parent if you stop labeling kids as passive-aggressive and so on, and stop looking at every single thing they do as "making it clear" they don't want to play.
Yes, you are moving, and that may be a good thing. But the same thing will occur in your new neighborhood if you view every child as a potential threat to your children's feelings. Kids have to learn to deal with things, and largely they do. You will be much better served and will have much more resilient children if you teach them not to take every comment, glance and action as a personal affront. It's just not healthy for you or for them.