There is doubt about the sequence of these cards.The first cdvs above may be from the first year or two: the ladies' hair partially covers their ears - a style of the early sixties, and the cards are the thinnest. The first is the only one not to mention the Bothwell address, where Robertson was from 1862 - 1865. Note that the graphic on the first is similar to that used by others at the same period, eg MacNab and Bald.
The cdv above is on slightly thicker card, so may be later, suggested also by the style of beard, and long jacket.
In the first cdv below the feet of the stand intended to still the gentleman's head during the possibly lengthy exposure can just be seen. The second gent is closer to the camera, which suggests a slighter later date.