I do feel sympathetic to them as I think the NT has gone overboard in this property.
The property was gifted to them by a man who was as far as his family, who are still alive, single all his life. He was incredibly private. This may or may not have been because he was gay and due to laws about homosexuality at the time - we can't know if he would have been just as private now.
The NT has had access to his diaries and discovered he had gay relationships and decided Felbrigg will be it's LGBT flagship property, with everyone wearing badges etc. His family are furious saying they had known nothing about his private life, he was a private person - they really don't care that he was gay but he wouldn't have wanted this this.
I would guess (hope) this is the angle the volunteers are coming from. I think the NT has looked at the past through the eyes of the present.