Not daft at all. He will bark at Fb vids I am watching, my friend often posts her GSD doing stuff and he comes over and starts giving it the full Monty.

Re getting between him and the Tv, that depends on the dog.
In some cases that works very well.

In others it's easier to start further away from the TV as the magnetic attraction of the "magic box" can be too strong to get any focus on your alternative attraction initially, until you have had a chance to build that a bit.

Re his wingman coming in, if you can focus on and manage the more reactive dog, the less reactive dog often takes care of itself (or at least only requires minimal effort), so long as the catalyst is out of the picture.

As part of your early desensitisation, depending how intensely reactive he is, you may find a light cloth over the screen helps, so the picture is less distinct.