We do that all the time with videos form Autel EVO 2 with the Autel live deck. I believe we tried it in the past with a tablet (our tables also have an HDMI output) controlling the Tello and on as Zoom session with a screen view. If I recall, it worked well.
Caveat: Works ONLY if the primary phone/tablet can forward the stream data to a secondary PC/phone/tablet.
If running an Tello EDU in AccessPoint mode (or however it is called when Tello & phone both connect to an existing access point) this should be no problem.
If running in normal mode where Tello is creating it's own Wifi then this won't work. While Tello allows two phones to be connected to it's wifi it does not route network traffic from one phone to the other.
Workaround: add a suitable Wifi repeater as it will allow traffic between all connected devices