i'm in your conscience
There are no Dark Pokemon during the main game of FRLG. You can't buy Max Revives either.
Anyway, you'll want good Electric and possibly Fighting types (or moves, cause it's good to have your Pokemon have moves of different types for coverage) for Lorelei. Dark moves you can get as well, as she has a Jynx and then Agatha later has Ghost types. For Agatha, you'll want a good special attacking Pokemon that's preferably not Psychic type, but has Psychic. Or if you want a Psychic type, make it a fast one, like Starmie. Starmie has great coverage movesets. If you get Starmie, have it know Ice Beam, Surf, Psychic, and Thunderbolt. Ace. Some of Lorelei's Pokemon are weak to Electric as well.
As for Bruno, he has two Onix so that Starmie I mentioned will be fine for his whole team. Lance will be weak to that Ice Beam. If you want a more bulky Water Pokemon though, you could go for Lapras, who can have the same set as Starmie that I mentioned, though it's not gonna have as much speed or power. But I know some people prefer bulk over force.
Blue is difficult to talk about since your starter determines his team, but once you get that sorted out, you can come back to ask more questions.