You don’t need two because you have two Veros. You might need two if you want to watch or record two channels at once.
Attach both to one of your veros, using a powered USB hub (they are quite power-hungry) and run tvheadend on that vero. Also, you will probably want to attach a USB disk to that vero for recordings. The other vero just needs to run the HTS add-on to view live TV or the recordings made on the TVH server vero.
Each tuner can tune in to one ‘mux’ at a time then each vero will be able to view or record any channel on that mux. Freeview provides at least 6 muxes.