I'm trying to hatch eggs for a shiny Pokemon right now and I wanted to know if Flame Body effects stacked in my party. So would multiple Pokemon having the ability keep halving the number of steps needed to hatch an egg or would it stay the same?
EDIT: I saw that this question has been asked but that was a while ago. I wanted to know if anything had changed since Generation 8. Thank you.
From Pokémon Emerald onward, if a Pokémon with Flame Body is in the party (even if fainted), the number of cycles it takes for all Pokémon Eggs in the party to hatch are halved. This effect does not stack with itself, Magma Armor, or Steam Engine; however, it can be stacked with Hatching Power Pass Power, O-Power, or Roto Hatch.
Unfortunately not.
Source
Hope this helps :)