Neither are old enough or obscure enough. There're still millions of people around today who know who they are, what they did, and have an opinion on them, and the majority of those people will hold negative opinions which is the main problem with the Dolphins.
(Beside that, Brothers are already bidding for an NRL license (not for a Brisbane club though), and the Diehards still exist, so you'd either have to buy their brand from them or go into a joint venture with them.)
If a bid was going to go the route of a "historic brand" then they'd need a brand that is much older, like one hundred years older, and that has fallen into obscurity, and there're quite a few to pick from if you have a look.
I mean I only grabbed out my copy of Our Game by Steve Haddan and and went through the first few years of the BRL and came away with a team called Natives, another one called Railways, and a team from Toowong who were known as the Cemetery-siders (definitely potential there), so there's plenty of potential to co-opt old team names and monikers.