On the ratio of slave-owning families in the Confederate South, this goes into a bit more detail, with slightly different numbers:
VIRAL POST GETS IT WRONG ABOUT EXTENT OF SLAVERY (Politifact)
But its numbers are slightly different. Whereas the above says about 33% of Confederate households owned slaves, this one said most states were about 20-25%, and a median across the Confederacy of about 27%.
The part about blacks who owned slaves was also very interesting.
