This should answer your questions.
FWIW, Colin’s initial experiment of manually attaching intercom wiring looks like it’s from 1978. And it’s almost definitely it’s a two-way thing.
The earliest car in the video using wireless radio is the Williams of Piquet from the beginning of 1986, it looks like. But then Mansell mentions a “Pacific” race where he and Patrick Head had a huge conversation in the radio, and he had to come from behind to retake the lead and win from Keke Rosberg. That was actually the South African GP in October 1985. So based on what I could find, there was definitely two-way wireless radio by the end of 1985. Not sure if it was around before that year.