ok here are movesets:
-Lvl 27 Roselia (Magical leaf, giga drain, GrassWhistle, leech seed)
-Lvl 27 Gabite (dragon rage, Earthquake, sandstorm, tahe down)
-Lvl 27 Monferno (flame wheel, ember, mach punch, feint)
-Lvl 27 Psyduck (hydro pump, water gun, Confusion, fury swipes)
-Lvl 20 Ghastly (Confuse ray, mean look, curse, night shade)
Can you also provide natures so I can see if they're worthy?
For Roselia, I recommend a nature that raises Special Attack (Rash, Mild, Quiet or Modest) or a Timid nature if you want extra Speed.
Gabite is physical-based attacker so I recommend an Adamant or Jolly nature.
Monferno's Attack and Special Attack are even so judging by your moveset, go with either a Naughty, Lonely, Naive or Hasty nature (avoid Timid, Calm, Bold and Modest as your Monferno has a physical moveset).
Psyduck is a Special Attacker, so I recommend Rash, Mild, Modest or Timid nature (avoid Quiet).
Gastly benefits from Modest or Timid nature (avoid Jolly, Impish, Adamant, Careful, Rash, Mild, Quiet, Naughty, Lonely, Naive and Hasty due to Gastly's low defenses and the former four reduce Special Attack).
Now, moveset wise - Hydro Pump is usually inaccurate, so I prefer Water Pulse until you get Surf.