Question about Philips Hue Ensis

No, there are two separately controllable lamps. Each can be controlled with its own colour and brightness.

You have to coordinate the app twice - as if they were two separate lamps. One for downstairs and one for upstairs. You currently only have one in your system.

You can dim the top and bottom separately. Either with Bluetooth or with the app.

No, both lights can be dimmed.