It is highly unlikely that random citizens of the town would have standing to bring a claim against you or the nonprofit simply because they don’t like what you have done to try to protect your collection.  Standing requires significant personal injury to someone who has a clear special interest in the situation that is above and beyond that of the general public. You haven’t said anything to suggest that they would have standing here.

In general, only the Attorney General of a state has standing to challenge the actions of a nonprofit board and they don’t normally go after an organization, and especially not against its individual leaders, in the absence of bad faith or clear breach of fiduciary duty. And your fiduciary duty is to your organization, not to citizens who may disagree. A lot of museums are struggling these days and a temporary suspension of activities may be the best way to save them.

I appreciate your sense of frustration with people who think they know better than you do, even though they have never lifted a finger to help in the past. There are a lot of people who think they own a nonprofit and should be in a position to tell it what to do.  Fortunately, the law is structured to protect stewards like you who in good faith are willing to provide their time, their wisdom, and often their money, in their attempt to improve the community. The law is not structured to support claims by know-it-alls who have no particular stake in, or responsibility for, the matter.