So instead of stuffing all those heroes into one film, why not take the two that are the most removed from the rest which are similar in many ways and have a movie about their lore joined? The Amazon vs the Atlanteans. You could have WW and AQ as the prince/princess of their respective kingdoms, or one is in power in the Kingdom and the other is second in command of the other kingdom, or both are in power and head to war with each other. Ares could be behind it all or something. There's a lot that could be done with it. Think something like Lord of the Rings cross Thor. In the end the two of them could have some sort of an alliance. It could easily introduce their backdrops without coming off as too dry, and doing it together won't seem too repetitive (as opposed to two separate films) and trying to explain their backstories in addition to the rest of the JLA in the JLA movie would be tough.