Johnson Brothers didn't become Johnson Brothers until 1883....so they post date that.
Johnson Brothers also had a factory in the US...what is the mark on the back?
I don't have a pattern dates for Johnson Bros....but you can bet it's out there!
I feel fairly safe saying they were made around 1900, give or take 10 years.
As to value? What you can sell them for. Check completed sales on ebay. My guess is you would be lucky to get $10 for all 4.
Linda C