I have experience with webRTC and would happy to help with this work. Based on features I’ve seen in paid offerings (like Twilio, Ringcentral, OpenTok), I’d recommend investigating open source solutions like: GitHub - onsip/SIP.js: A simple, intuitive, and powerful JavaScript signaling library
Alternatively, rolling your own webRTC interface may be a good idea: GitHub - webrtc/samples: WebRTC Web demos and samples - especially if you want to host a STUN/TURN server on your own, HIPAA-complaint premises.