OP you've taken a bashing on here.
I get your point about the ignoring and rudeness.
The trick is to not react or give it a second thought.
There are always rude people, in the playground, office,shopping centre, everywhere.
I have worked in the same school for ten years. Most of my colleagues are great, but there are a few who never return a "good morning' in the staffroom, or say thanks for opening a door for them. One teacher in particular is so rude that it's laughable. But he's the one with the problem.
Stay the same as you are, greet everone with a quick good morning, and feign indifference if they don't respond.
The only thing worrying about your thread is that you care too much. If it was a family member or a friend snubbing you, then fair enough. But these people are just a group of random people who have kids the same age. Those kids will form their own friendships, sort out squabbles, keep their distance from those they don't like, it's how we learn.
Invite the class, be polite to all, and don't react to the rude parents.
You need a tougher skin to bounce it all off. Be proactive, be friendly and polite because you have standards and are well mannered. Don't dignify the ill mannered people by reacting or giving them a second thought. They're not worth it.