Bit about there being two legendary devil fruit is interesting. Fact that there are two for one is intriguing.
That in addition to the fact that Rocks thought they were necessary in order to topple the WG.
We know one of them is whatever was on Elbaf which someone apparently stole when Harald died but wonder what the other one is, the Nika fruit maybe?
On Elbaf's legendary DF currently it looks like an outside party might have stolen it
Maybe even someone on Rock's crew that was privy to this knowledge given they are said to be mercenaries but I feel like that could be a red herring in order to make us think that Loki doesn't have it when he might in actuality. Could be that Loki killed whoever stole it and ate it right after it was stolen. Hence why the people of Elbaf say that he has it? Plus, with this new info of those two dfs being necessary to toppling the WG, I can't help but feel that it'd also be necessary for Luffy to have it under him in order to be able to topple the WG so again, Loki currently having it makes a lot of sence given he's very much looking like an ally/nakama.
Lastly on Rocks, the fact that he wanted Harald to eat the DF and not himself could be an indication that unlike Teach, he's unable to utilize more than 1 df