The thing they have to fight though is that when you register for a trademark, it doesnt apply to every sector. Apple cannot for example and sue farm conglomerates for using the word apple on their actual apples. They do not hold the trademark in terms of produce.
For example, Nintendo lost a trademark to a supermarket in I think costa rica named "Super Mario" (it was a supermarket owned by a guy named mario), because Nintendo did not own the trademark rights to supermarkets(however they held one for food products branded it, so the same supermarket could not name their home branded products super mario)
Its a matter if the band holds the trademark for movies, as the band in the show itself is not called Demon Hunters (its Hunter/x)