I have had all four of those varieties in my orchard. Discovery is an early, the other three are mid-season apples. I now only have Jonagold, James Grieve, Granny Smith and Bramley now.
Discovery and Cox are in the same pollination group - B, while Golden Delicious is in group C and Jonagold is in group CT. (A is the earliest to flower and D the latest.)
The T stands for triploid, which means that Jonagold needs two other varieties for pollination. Golden Delicious, as a parent of Jonagold, will not pollinate it. So expect your Jonagold to be unreliable unless there are crab apple trees in the area. Crab apples are really good general pollinators.