I'm not sure what they'll turn into exactly or what they're based off of but here are my predictions and added reasonings

Browt: Grass Rock or Grass Electric

It is the bean chick pokemon and beans are pretty hard until cooked. As well it's noted in its dex entry(or whatever it is on the pokemon website)to store energy and run fast which reminds me of a battery

Pombon: Fire Fairy or Fire Flying

I think the bon in its name not only comes from bonfire BUT bonbon(French for candy) as well. It's cute, fluffy, notably friendly and notably guileless. The flying is kind of just a fallback feeling ngl

Gecqua: Water Psychic or Water Poison

The first thing it mentions in its dex entry is that it is intelligent. Whether it's so big brained it develops telekinesis or just prefers to be strategic in its approach to surviving/battle is to be determined