Does the H1 chip (in Airpods 2 and PBP) support streaming from one device to two sets of earphones? I remember reading somewhere that the new H1 chip supports streaming to two sets of earphones simultaneously from a single device.

That is, you can have one source device that's playing audio, and two sets of airpods would be able to hear that audio at the same time.

Is this a feature of the H1 chip?
I think you’re referring to Airplay 2, which now allows compatible devices to Airplay to multiple devices (such as both your HomePod and your Smart TV).

AirPods use Bluetooth, so this does not apply unfortunately (Airplay uses Wi-Fi).