Try using the Buffer tool to buffer the points to a tolerance, dissolve to create single polygons for each cluster, and then use a join to count the number of points in the cluster.
Then use the ratio between the area of the cluster and the number of points to apply your parameters.
Best Answer
The solution is quiet straightforward : Using the NNjoin plugin i made a self join of the house layer using the distance criterion
the result layer gives the distance between the houses!
a simple query gives all the houses within a 5 meter distance "distance" <= 5
An alternative solution can be to use the v.cluster from the grass toolbox !