Thought I'd resurrect this as there has been no focus on the silent era recently.
Cary needs to be scrubbed off your list @drol. Also, Wiki users have agreed to remove Donnie "Beezer" Smith from the list. There doesn't seem to have been evidence of him being alive for years now. I think the last time something concrete appeared was 2004(?).
So that leaves just 5:
Don Marion Davis, 102
Silas Hathaway, 101 (though not confirmed alive since he was about 98?)
Mildred Kornman, 95
and the two remaining Watson siblings: Billy, 97 and Garry, 92.
Will 2021 be the year when the silent era loses the last of its screen cast?