Le or le, what is le answer?

Not necessarily strictly business related, however I do like to get writing standards and protocols correct.

Is it le Roux or Le Roux?

Some time ago I read the following writing guideline, which I really like and have been using since. However after a conversation with a couple of Le Roux’s, few know about it, so any guidance will be helpful. Google has also not been too helpful.

Here goes: sons all get the capital “Le” and daughters the little “le”. If you marry a “Le Roux” then the wife also becomes a capital “Le”.

What is the correct use of a seemingly basic surname?