Hi, and my deepest sympathies.
Advice is hard to give, but my first thought is to run away as far and fast as you can. You won't win this if the board is so entrenched and closed off. You don't mention if there is any organization the board reports to, perhaps help could be found there. Another direction is to seek out other gardeners with whom you have established good relations and work as a group to find the truth and make the board accountable or vote them out. I also had a miserable time the last few years in my garden, but there is nothing worse than being stabbed in the back when it appears to be just a power and personallity clash. Best to you - I'm sure others will have wise words.
Lisa in Mpls.