One Piece Theory: New Strawhat and Big Mom VS Vinsmoke Family (Chapter 816+)
Lets start with Fishman Island, where Luffy gave the treasure of the Royal Family to Pekoms and Tamago.
This is allowed Tomago to convince Big Mom to wait 2 weeks. This meant the Tea Party was probably postponed.
The Tea Party about to take place is the one where Sanji is getting married to Purin. Who is likely the girl above. She has 3 eyes (3 is San in Japanese) and is setting on what looks like like a throne.
We know that amongst the treasure is a Tametebako (box) filled with explosives, as told to Neptune by the Minister of the Right (seahorse).
I think it is safe to assume that the box has not yet been open, as Big Mom has not contacted Pekoms or Beg.
I believe that the Tametebako will be given to Sanji’s father who will open it, causing an explosion to occur.
I believe this will spark an epic fight between the Vinsmoke’s and the Big Mom Pirates (Won’t last long). This will either allow Sanji to escape or the Strawhats to sneak in.
And I also believe that Purin is not directly related to Big Mom. And that she will probably be the next Strawhat.
And yes I am aware that quoting Luffy on this matter is the worst evidence, as he expected a tree and a unicorn to join. But hey, I can dream.