Go to the City Council meetings. Shout very loudly! Not literally, but make your voice heard by participation. Okies are so polite, so very nice. It is not disrespectful to question the Council in minute detail in everything they do, especially when they have a history of usurping your authority over your own land.
Get the City To Pay for easements, buffer zones, and land use restrictions. If they covet all the stuff they say they do, the only right and just thing for them to do is obtain it through eminent-domain laws and just compensation. The cost to do that would be extraordinary - they could never find enough money.
Point Out that the Greenbelt Commission recommended purchasing (instead of stealing) the rights to do all the stuff they want to do.
Get the State of Oklahoma involved. Contact your district representative. I don't know if the State has any standing or not. They did give you the deed to your land.
Community organize? Egad!
Get the city charter amended like these folks: Former council members suing city over petition
Visit Democrats Against Agenda 21 for ideas.
Council or Mayor Recall. Surely there is a way to initiate that action.
After they've been caught, and booted out, you are going to have to go back and clean up the city code. There must a mechanism to review all the acts of a city council going back so many years.
You could get the city charter repealed, and a new one written. That may not be as hard as it sounds. The new charter would have to assume all the financial obligations of the current city.
Once they are out, and you've cleaned up the code, you and your children are going to have to keep a watchful eye on them returning. You will have to do this for the rest of your lives, sorry.