These are not “golden retrievers,” as Christie’s claims. The true golden retriever program wasn’t underway until the 1860’s.
The painter was John Hamilton Glass, and the painting appeared in the Scottish Royal Academy in 1852.
The dogs are fairly large, and the one in the one in the background looks very much like a British conformation type golden retriever.
You can tell they are retrievers because the game presented are a pheasant and duck.
Yellow retrievers existed long before the true golden retriever came about.
And no, that terrier isn’t a Jack Russell, but you could call it that and not be entirely wrong.