@FailForward
My TV Headphones are bluetooth, they come in a set of two - ie. (a pair of(a pair of(headphones)). They both *separately* connect to one little broadcast thingy, which takes a single input and sends it to two headphone receivers simultaneously. So, what you want already definitely exists. At least, for TV-watching headphones it does, anyway. Brand name = Avantree.
@FailForward
Cable.
Your hub may not exist ... yet. You might be just one of the earliest customers to have identified the need. The market will fulfil the need eventually, when there are enough numbers of buyers with the demand.