"And of course in writing this I also feel like I am not a "nice" person by not trying to "help" them or be more "understanding", etc., like I am a big "B". "
First off, M., no one can be helped unless they want to seek real help. And for them, it would be with family counseling and other professional resources. I'm pretty sure you aren't a certified therapist, so don't feel badly about not offering your services in that area.
If you want to continue to have a good relationship with these folks, here are a couple ideas:
"Our yard, our rules". Each and every time the kids come over, stop and take a 'rule break'. Write the rules on something so you can remember, and keep them positive:
We ask before using the toy our friend is using.
We use our words to solve problems, not our bodies.
We ask take turns with toys and ask for a turn "when they're finished".
We are safe with our bodies and our words.
Our language and our bodies are friendly and safe.
I would actually put these on something smaller but permanent, so they can be visibly read and posted during playtimes. Review them EVERY time, right in front of mom. Notice that the 'rules' are very positively worded.
Then, stay child-focused when the other mom is over. When she drones on and on, keep your eyes on the kids, not her. Actively parent your girls, and step in with confidence if you see some unsafe actions on the part of her girls. Narrating the situation helps better than jumping into a correction: "Andrea, I see that Josie is using the shovel right now, and that your hand is on it because you want to use it too. Andrea, ask Josie 'Can I use the shovel now?' Oh, so Josie, you aren't done using the shovel. So Andrea, you may tell her 'I'd like a turn when you are finished, please'. There. Josie, when you are finished, Andrea would like that shovel."
Notice that all the language in this example is *very purposefully neutral*. You aren't saying Andrea's being pushy, you are simply cueing her in to your family's way of doing things and correcting the situation as you go. Thus, less for this other mom to argue with.
Your three year old isn't going to understand, either. Sorry. She just sees them as "big girls to play with". You can also use the "oh, we are having some family time right now" line, which is polite and respectful while letting them know that you don't want visitors at the moment.
And fences are also pretty awesome!