This is what I remember – a group of friends went on a trip to the countryside and stayed in a house together. One of the rooms was described in great detail with lovely furniture, all child sized. It was the room I craved the rest of my childhood. There was a tree house, and an orchard. They met up with gypsies, and I think a fairie ring was involved somewhere. They were all friends from the same neighborhood. Do not recall if any of them were related. I read this book before 1968, it was not new.
Could this have been The Chateau Holiday by Winifred Mantle? There are several books about the same two families of kids who go traveling together. I don’t remember a fairy ring, but I’m pretty sure there was a small house, a tree house and an orchard, although those may have been in different books. Some of the other titles are The Painted Cave, The Hiding Place and Tinker’s Castle. They all has some mystery element as well. There were at least five kids (maybe six or seven) in two different families from the same English neighborhood.