I don’t think you can really get away from the tropes when you pick twins, given their situation. There’s plenty of “evil twin cases” as well in media. If anything I would assumed twins not getting along would be more prominent. I’ve started to see some instances where twins exist in a medium, and they are just there and not the main focus as well.

As for lore breaking, I think the show breaking their lore would be fine. Having a third show that follows the rules strictly would get boring. For the franchise to work it would have to keep evolving and growing. We already had Korra break and restart the avatar cycle, so no one can connect directly with the lives before her anymore.

I’m surprised they are able to use the Avatar name again. They had to drop it for Korra due to James Cameron.

I was also hoping the show would have dual avatars as the twins, each with two elements. It would solve some of the story roadblocks of them having to find reasons why they can’t just go into the avatar state all the time. Would have been cool if the avatar state only worked when both of them are next to each other.