We love restoration projects where all the original details are there to be admired .... and copied.
Having the original castors (on one of the chairs) is important, but seeing the positioning of the upholstery nails (three different sizes on the chair with the 'hay arms' !) is also key to a good restoration.
One chair has it's orginal seat cushion missing, the other has had velvet seat and back cushions added, probably in the 1930s. Velvet would still be a suitable contrast to the leather, and something we can repeat, or we can reintroduce a leather feather/down filled seat cushion.
We can, of course, change the colour of the leather, but a good 'English tan' would seem to be most appropriate.
I have included an image of a fully restored, not dissimilar pair, as an example of what can be done.