To recap the structure you described, you have a many-to-many relationship between House and Kind of Room types, and there is a repeating field group (with fields furniture and furniture year) belonging to the Kind of Room posts.
The m2m relationship has an intermediate post type to store relationship fields.
Visually, the relationships look something like this:
house << intermediate >> kind of room
|
|
furniture RFG
When displaying the house post you are able to list the connected kind-of-room posts ordered by the number of such rooms by using a View which queries the intermediate post type with a filter for the related house post.
You want to display the furniture RFG fields for each kind of room output by the previous View.
The problem is that the previous View is not iterating over kind-of-room posts, it is iterating over the intermediate posts (but outputting fields from the kind-of-room posts using the item attribute to switch source).
So when you insert the second View—to display the furniture RFGs of a house—we need to tell the View the kind-of-room post which should be used as the owner of the furniture RFGs instead of the intermediate post type which is the current post in the parent View loop.
In my screenshot you can see the Query Filter for the View to display RFGs, I'm telling it to get the ID of the post the RFGs belong to from a shortcode attribute (wpvrelatedto by default, though you can change this).
Then in the parent View where you insert his View using a shortcode, you provide the id of the related kind-of-room post rather than the intermediate post, e.g.