My brother has gone on a cruise, and he is posting his photo's (look where I am),on Facebook. His address is readily accessable (along with a lot of other personal details) from this and other websites.
By advertising that the house is empty, I think he is asking for trouble.
I think that you are getting unnecessarily paranoiac.
Of course there is a risk but it is not nearly as large as forgetting to cancel the milk.
Unless your brother has contents worth £Millions, few thieves would spend the required amount of time researching such an operation. Of course, if he has a van Gough or Turner on the Sitting Room wall, it would be a different matter.
If someone on-line can make a connection then lets hope his insurance is in order.
In France ,Cantal region,whilst travelling there my sister in law pointed out markings on empty housing not a sign of plague, as in years gone by, but information to certain travellers that this property was empty and ripe for 'content removal'.