A few sets might help. 1) both android devices must be connected to the same wi-fi. In car it can be done by turning on hotspot functionality on either device and connecting the other to it. Then there are two types of applications, first is VNC. Install a vnc server on the tablet (search on google play for vnc server) and a vnc client on the phone (RealVNC or other). Connect from the client to the server and you should get the tablet's screen on the phone. The other type of apps is DLNA/UPNP variety. Try to install BubbleUPNP app on both devices and stream the phone content (video or else) to the tablet as a receiver device. You can try Twonky mobile apps too. Another pair of apps is cheapcast to the tablet (the app not available on play store, download from the internet) and localcast to the phone and stream from the phone to the tablet. Another one to try is Allcast player and receiver apps available on play store (paid apps).
2) if both devices are connected to the internet separately, download Cloudcast to both devices and pair them in the app. Mind its a paid app too.
Hope it helps.