How can I query overpass to get data in counties->municipalities?

It's currently not possible to restrict an area query with an area, so it is necessary to use map_to_area calls to work down through the areas.

You can see at the top I've commented out the code to fetch all the admin_level 4 entities in Norway and instead just fetch 1 of them, because the script times out with more than 1. Anyway, this script emits the tags for each admin_level=4 and then emits the tags for each admin_level=7 and then any place=farm found within that admin_level=7. So processed as a stream, each farm will belong to the last seen county and municipality.

[out:json][timeout:150];
//area[admin_level=2]//["name:en"=Norway]->.country;
//(way(area.country)[admin_level=4];
// rel(area.country)[admin_level=4];
//)->.counties;
( rel[admin_level=4][name=Nordland];
  //rel[admin_level=4][name="Trøndelag"];
)->.counties;
foreach.counties(
  out tags;
  map_to_area->.countya;
  (way(area.countya)[admin_level=7];
   rel(area.countya)[admin_level=7];
  )->.munis;
  foreach.munis(
    out tags;
    map_to_area->.munia;
    (node(area.munia)[place=farm];
     way(area.munia)[place=farm];
     rel(area.munia)[place=farm];
     );
    out center;
  );
);

You can also look at https://github.com/drolbr/Overpass-API/issues/187 for some discussion of how to fetch points with containing areas.