What are these streamers? What is their function and purpose?
Combination of:
a) Functional equivalent of headphones, wirelessly streaming audio from a line input or Devil's Lesser Radio device to the hearing aid.
b) Radio aid, providing a microphone that's closer to the person(s) you want to hear than the one on the hearing aid itself, which improves the SNR.
In ye olde days, (a) would take the form of a cable with a 3.5mm headphone jack on one end and a fiddly little plug on the other. Obviously this Just Worked, so was ripe for replacement with complicated wireless solutions as soon as technology allowed it.
(b) Would take the from of a dedicated receiver unit, connected to the hearing aids either via the above cable, or an induction loop worn around the neck. An FM (or latterly, digital) radio transmitter similar to those normally used for wireless microphones for public address or filming would provide the signal. You may have seen barakta using one to hear me on bike rides.