The mediaeval houses are roughly square in their dimensions - approximately 165mm x 165mm internally and 183mm x 183mm externally - and so need a square baseplate. The house and barn are, of course, not square overall, but, if I remember correctly, have an internal cross piece for strength, whcih makes them effectively made up of two squares. So the answer would be, "No" as regards using the baseplates with the mediaeval houses.
Edited because I was only answering the first question asked by retronio22 and not the second.