Sorry if this has been covered before, but here is an Interesting article in the Connexion on how to obtain a carte de séjour UE – séjour permanent. This might be handy if Brexit really occurs but, of course, there are no guarentee's. We will probalby give this a try.
Here is a link to the article:
http://www.connexionfrance.com/carte-de-sejour-permanent-prefecture-Brexit-12195-news-article.html
Tony