how to deal with people who think they are always in the right?

How would you deal with people who are blaming you for things you haven't done, are saying they said things when in a room of 9 people only 1 person (their friend) heard them say it and making decisions that aren't theirs to make. Ive been accused of holding secret meetings (they openly have meetings outside the school gates on most days, non of the content of these meetings is made public to other members), making decisions behind their backs, changing things that have been agreed, altering minutes to not reflect what was said in our meetings, not respecting other people's views and not being available to speak to. I have had 'secret meetings' with another member of our group but I basically moan about the rubbish that these 2 members are spouting. I have made one decision without their approval but I based my decision on their input and did what they wanted, I type up the minutes from the meeting and at worst I rephrase sentances so they make sense (for the people who were unable to attend), I haven't respected their views by not agreeing to a meeting so the 2 of them can moan about me but I offered to speak to them in person or via email instead and as far as being unavailable goes I see them every weekday and they have made no effort to try and speak to me at any point since December. I'm at the point where banging my head against a wall would be more productive. This is in regulates to a school pta. I am the chair and I also work at the school so unlike them I can't resort to name calling, I have to be diplomatic and respectful. I really don't need this stress while we are TTC!