WanderingWendaline
Farmer
Before looking at everyone else's theories, these were my first thoughts:
1. The two paths are the Community Center and Joja Co.
ConcernedApe has said before he wishes he made the choice more nuanced, and the choice doesn't even affect the game that much later on, so I think that makes the most sense.
2. There are a lot of different things in SDV that come in threes, but my first thought was a new dark shrine in the witch's hut.
3. Mermaids aren't mentioned much in-game, so that gives us less to speculate on... Something with pearls??? I dunno
After reading other theories, something with kids does make more sense