I wonder if it's the headphone. Fro the TV try a basic wired headphone that plugs into the audio jack. Does that give the wrong audio also when watching a show you're watching on demand form the Xfinity/Comcast box?
The iPhone/iPad issue, as you describe it, has nothing to do with the wireless headset, since you say "earbuds".
I have a wireless headphone set with a base transmitter plugged into the audio jack on a Samsung ( not smart TV) LCD TV.
When watching all normal TV channels the headphones work however if we watch a show on demand, the audible sound is not from the show we’re watching but from a base channel? ( we have a Xfinity/ Comcast cable box & service)
Also, when streaming from a Apple TV unit the audio is not correct and if I plug earbuds into the iPhone or iPad that we are streaming from, then the streaming picture stops but the audio works.
I need to get headphones that work with all audio since my wife has trouble hearing. Thanks!