Will the masuda method work with pokemon from fire red to diamond (in my case) or from any gba to ds?
With eggs hatched from pokemon from another game, is the masuda method still in action wih those hatched pokemon if they breed?
No. Masuda Method only works when you breed a Pokemon from ANOTHER LANGUAGE with a Pokemon with a different language in your game. Like breeding a Japanese Charizard with a American Charizard.