Thanks very much for all the replies. You've cheered me up quite a bit.
ssomon, you are correct, I don't have any control over who enters the property, and there is no will. Yes, it is a very sad situation. What I've told you is just the tip of the iceberg.
Harnser, thank you for the link, which is very interesting. Since there is no will in this case the change in the law will not affect my family.
Gluestick, the house is in France. There's no will. I don't know what the size of gross estate is. My brother's notaire said probably less than a quarter of a million Euros.
Alan Zoff, of course the notaire should be impartial, but will he be? I have been using Google Translate to send email in French, and to understand the French email I get. It works fairly well. It's quite fun and good for my French. I thought a notaire was a lawyer, not a judge. Is the line between judge and lawyer blurred more in France? Is a notaire somewhere on a spectrum between the two? I heard that under the code Napoleon or something the judge is also the investigator, like in Almodovar's High Heels (set in Spain).
Talking in a friendly manner is always a good idea, surely? The French appreciate it when you assume that the default language is French, too, I think.