Shut Lock and Load People

I am not currently living in my house.  It is rented out to people as I travelled for eight months and upon my return, I moved in with family (back to Chisholm I go).  This weekend when the extended family gathered for a family tragedy we offered beds to others and they were quickly filled.  At one point in time we had 11 people sleeping in a four bedroom, three bathroom house.  A tight squeeze but that is what family does for each other: provide beds, toilets, showers / baths, food, good conversation and a stellar game of bridge.

After two days I noticed a trend in my extended family: eveyone used the toilets but some did not know why there was a modern day shut door / turn to lock combination attached to each bathroom.  My eyes experienced the following in a 48 hour period:

1.  Walk in on uncle on toilet at 4 am. 
2.  Walk in on aunt on toilet at 10 pm.
3.  Walk in on mother doing her business, repeatedly.
4.  Walk by bathroom to see sister using facilities, 12 pm.

Yep.  Seems the door / lock combination is too advanced for my family.  Perhaps I should spend the spring building an out-house in the back yard with a wooden sign that says 'free' on one side and 'not available' on the other?  Do you think a quick flip of a wooden sign would save me from the intimate details of my family members?  I still love them all, it is just none of my business what they are doing in the secrecy of their alloted bathroom time.  Now how do I gracefully breach the subject with the offenders, loving family members?

(Pictured copied from Google pictures: thecoffeedesk.com)