This is possible but I am also currently under the believe that is merely an urban myth.
Unfortunately, it's no myth. This is off-topic, I won't try to convince you here. But when you have some time, try to read up on it (use reliable sources, not facebook posts). A lot of health issues are like that: you slowly kill cells that don't grow back (right), but it can be years or decades before the effects are felt. If you enjoy loud music (hell, why wouldn't you?), try not to put it straight in your ear.
As for Bluetooth, it just doesn't work like that:
https://en.wikipedia.org/wiki/Bluetooth#Communication_and_connection
A headset (slave) will connect to one source (master) and that's it.
What you need (mixing sources) is easily done in software on a laptop for example and then you can connect your headsets to the laptop doing the mixing. Unfortunately I'm pretty out of the loop, I don't know which software would be best for grabbing sound from multiple devices before mixing. I'm sure you can google that, tho.
Also, if you're really into music, do invest in a pair of good headsets. You'll be amazed. It's not hard to score a good pair for $200. You can also walk into audio stores and listen to various models before purchasing. In fact, I strongly recommend you do, sound quality is highly subjective, nobody and no amount of tech specs can tell you what sounds good to you.