We were able to find a way to have a happy medium by asking the teachers to select someone that would be able to represent them at our meetings and the school baord meetings as we have our own school board.
Since we are K-12 each "school" has at least one rep (the elementary school has two to take turns)that attends or is in contact with the PTO.
You know, to expect everyone to come to a meeting.... ....I don't even expect everyone on a guest list when planning a birthday party!
Our last prez thought all the staff needed to come to our meetings to get our support, needless to say, that mentality doesn't last long or you wind up having no chance of a good relationship with staff. We have committees that staff are asked to join, this includes meeting groups, family activites, and staff social committee. Our principal has a sign up for these at the beginning of the year and PTO is one of them. She asks for one rep from each of the 4 pods, or sections of the school, and one additional staff person, such as a music teacher. Usually the Principal or Asst. Principal attend as well. The pod reps are supposed to report back to their pod anything that should be known for the month. This isn't perfect, only half of the signed up staff comes but we used to be lucky if we had any staff before that!
The irony of commitment is that it’s deeply liberating-in work, in play, in love. The act frees you from the tyranny of your internal critic, from the fear that likes to dress itself up and parade around as rational hesitation. To commit is to remove your head as the barrier to your life. --Anne Morris
Having the entire staff attending meetings is unrealistic. I am not sure why your group thinks that is the norm. Most schools do have no teachers that attend.
This is what our school does and it works out really well. Maybe you could see if you can establish something similar. Every year we have two teachers (every year the 2 teachers switch) who act like liaisons to to the PTO. One of them attends each meeting (they take turns). They bring to us any concerns, questions, or suggestions that the teachers may have and they also inform the teachers of what went on at the meeting to keep them in the loop about what is going on. Maybe you can talk to the principal to ask if they can help you do something like this.
What you need to do is extend a hand of friendship to them and let them know that the group is different now and would like to have a good relationship with them as it is beneficial to the students and the school as a whole.
I have been down this path, we had a group that the principal ended up dissolving. This group would bash teachers at their meetings even if there was one sitting there. They were very exclusive yet complained that no one was getting involved. It has been a long road but we are slowly getting to a normal realtionship that we all respect each other. Start slow write a letter talking about your new goals that include them ask the teachers what you can do for them not just monetary but volunteer wise, make little gestures like a lollipop ghost on halloween with a cute saying on it, a ornament at Xmas time, things like that. Be willing to share minutes with them, even financial about what your group spends money on, that always seems to surprise our staff. They dont know what we do until they see it all on paper. If you know a grade has a big project coming up ask if there is anyway to help them.
In reality do you really want all of your staff at your meetings? No that would be way to much, talk to your group about having a primary rep and secondary rep. If you are having fun nights and there is a teacher who has a talent(art teacher doing face painting, etc) ask them if they would be willing to help, they generally are willing with enough notice. Things will slowly change withing time, building that relationship takes TIME and do it slowly. Dont let the clique control you, teachers do have lives outside of school, they have kids, etc. I know in my school alot of them do volunteer work for their kids and their kids pto's. We seem to not think of that, I am happy if each staff member helps with one thing throughout the year and you know what? most fo them do...good luck take time!
Our PTO has ruined the relationships between the Teachers and Parents. The PTO seems to be a clique and the Teachers are becoming less supportive of the PTO's projects. The main Problem is our leaders think that all teachers should be at every meeting.
Is there anyone who has been down this road?
Does anyone have a letter that might be used to break the ice with the teachers? What is my next step?
....I don't even expect everyone on a guest list when planning a birthday party! 
