Well all seems to be well.
We have just returned from a second visit - who knew that the house was quite that wonky, definitely a rhombus not an oblong.
We went to see the notaire to see if there was anything that we could sign that would agree the house sale to us and his advice was to send a letter outlining our position and telling the owner how easy it would be to sell the house and that he would do everything - for the fat fee that we pay him. Leave a paper trail.
We have rushed around getting a letter written in a suitably french flowery style to say that we loved the house and were so sorry that the owner had such difficulties etc etc.
Cousin seemed to be falling over himself to say that everything would be well, much more concerned that we wouldn't wait until the new year when we return to France to buy the house.
Such a relief to have a house that we really like at a sensible price. And such a relief not to have to keep looking.