Could you please give more details on just what you're trying to do and what kind of set up you have -- smartphones, TVs, dongles, etc. -- because right now it sounds way too convoluted. References to a Chromecast indicate some kind of home use but pairing up with a car display indicates something in a car. Or are in a mobile home?
Something like a Chromecast can connect to hotspot, if it's currently set up to work on a home LAN you just have go through the set-up process to pair it up with the hotspot network instead.