helmet with built-in … headphones? …
We use them for an entirely different outdoor sport, but I will mention the Cardo
We use Cardo PackTalk Bold but any of the other models that cost less should also provide Bluetooth audio link to smartphone and work with whatever audiobook app one prefers. The Cardo DMC mesh radio tech is used to communicate between people at a distance. Bluetooth is always used to connect to your own phone.
The Cardo radio modules are an add-on to whatever helmet you have. Most of us use a full-face helmet with clear windscreen (similar to motorcycle/motocross). The flat disc speakers are inserted into the ear areas inside the helmet, and plug into the Cardo radio module.
Cardo also sells an over-the-ears headphone kit, to which the Cardo radio unit clips. No helmet.
Cardo is probably overkill for what was requested for hiking, but I suspect similar products exist for bicycling, with or without the ability to talk to other riders at distance.