Twilio Video uses WebRTC, so you would need to convert your RTMP or RTP stream into WebRTC somehow. I'm afraid that's all I know though. There's some interesting articles online about that conversion but not covering Twilio Video. It's probably a good start though.
Good day.
In this post, the topic starter mentioned Twilio client API.
We usually suppose SIP as RTMP function to republish Twilio SIP call to another RTMP server. Another option is SIP as stream function, in this case SIP call stream is published to WCS server as WebRTC, and can be played or republished to another server.