Sorry Sandra, I don't think this is the line I'm following. I've also searched my records for any free people of color in Stokes named Martin and haven't found any, so I suspect that you won't find Henny and Richard in the pre-1870 censuses. Also, the search for the last owner will probably require some archival research in Danbury, since in 1860, people named Martin held a total of 122 persons in bondage.
One lead worth exploring might be Alexander Martin, a Danbury farmer who is listed with a 21-year old mulatto woman, as well as several mulatto girls around the age of Victoria (6 in 1860). Interestingly enough, Alexander seems to be unmarried (it looks like he's living with his father Hugh and sister Sarah/Sally) and many of the slave children are mulattos.
All of this is conjecture, of course, but perhaps some Martin estate records could help. I'll keep an eye out in my own research. -- Gordon