Architect.

The Carriers must send me a private message one by one
As long as no one goes back to back
Each time, they request a letter and bring it back to you
Once you have enough letters, or you think you have enough letters
You, the Architect, must message me that you are done carrying
Your builders must unscramble the letters and make 2 words
Each has to post one of the words (not the same word)
First tribe to have both words posted on their challenge thread, by their builders, win immunity