tvheadend is 'back end' PVR software- XBMC/Kodi is 'front end'. Think of it as server and client.
You can theoretically run both on the same box, but it's more normal to run them on separate devices: one backend TV server with multiple front-end clients, for example.
I believe there have been ports of tvheadend to run on Android, but it's more normal to run it under Linux, either on a PC/server or on a NAS that also stores all of your recorded/ripped media (i.e. the Kodi library contents).
So... yes, you need a device to run tvheadend on; yes, you'll need hardware tuners to receive over-the-air (DVB-S/C/T) signals; yes, you might be able to run it on your Android device, but a Linux distro would be easier if you have the hardware; yes, you'll have to do some searching if you want to use Android as the server OS (it needs to support the tuners as well).