Also...I would say "become incapacitated." Because "become a burden" is loaded with negative connotations. I think there are lots of us here that would say that caring for another person is a privilege of inexpressible value. And that the person is not a burden but a sacred trust.
The people who need to know know. My POA, my HCPOA, my significant other, his brother and sister, my cousin who is close, four of my BFFs. I don't have kids or they MOST ESPECIALLY would know as well.
Only my sig other knows, since I have no siblings nor children. It's all written out in my Trust, Will, POA's, etc. therefore my Elder Law Attorney also knows.