The flowers aren't self-fertile, so yes, you will need to have at least 2 plants if you want fruit. I don't think you would need to plant both plants in a single container, however. The plants grow quite large, sometimes as much as 6' tall and 5' across, so putting two in the same container would probably crowd them too much for them to flourish. I also expect that a plant that size is going to require a rather large root system. I'm not sure a 9" deep container will be optimum for even one ground cherry plant.
Personally, I think your plants will do well if you treat them like you would a tomato plant, i.e. provide each with a container no smaller than a 5-gallon bucket, don't give them too much nitrogen, etc. You can place the containers all in one area, so insects can readily fly from plant to plant and provide pollination.
"Isn't it enough to see that a garden is beautiful without having to believe that there are fairies at the bottom of it too?" - Douglas Adams