Best way to connect 2 bluetooth headsets to each other? RasPi as gateway?

I have 2 pairs of Bose QC35 bluetooth headsets. I'd like them to be able to talk to each other. In theory, it feels like it should be as simple as getting a RasPi, 2 bluetooth dongles (or use onboard + 1 dongle) so both can pair to the RasPi at once, then with some software making the line-in from one go to the headphones of another, and vice versa.

I've spent a while googling but can't find any reference to anyone having done this. Not with a RasPi, not with anything. There's a few proprietary "bluetooth intercom" systems for motorbikes etc, but I want to do this myself.

Has anyone done anything like this, or have any ideas? Which language/libraries would be best to write an app that "marries" both bluetooth connections? I'm very new to non-web programming so I have no idea where to start.