Check the "Print and Visual Media Discussion Tent." There are forums there for both fiction and non fiction books.
@OParks, I think "Authors' Club" is intended to focus on upcoming book releases rather than as a spot for current and future writers to get together (I'd be willing to moderate such a forum if there was one!). I've only got the one Civil War book out, although it's actually my fifth published book - the other four are published under my - "ahem" - maiden name. Publishing in general is rough, especially right now when a lot of the publishers have been locked down since March. Given the current swing of the political spectrum, I'm asking myself if my next book should be another Civil War book (I was looking to do another one on Andersonville) or it I'd be better off changing genres.
Getting published the traditional way is hard. As we said in the conversation above, publishers don't want good books, they want profitable ones. You may be better off writing it, trying to sell it, but having a contingency plan to self publish it if you can't find a traditional publisher. I'm probably not the best one to ask about marketing - my book came out two days AFTER I went into lockdown (a student's mother tested positive for Covid, and that was our last day of school for the year). I had 2 presentations a week scheduled from mid-March until July, when I was going to lead a tour of the prison site for the NPS, and every single event was cancelled. It's a tough time to have a book come out.
But I think you should write yours anyway. Hopefully, by the time you finish, things will be better, and you absolutely should preserve your ancestor's story for future generations.