For an in-game Meganium, I prefer a more direct set:
Meganium
• Swords Dance
• Seed Bomb/Razor Leaf
• Return
• Earthquake
Razor Leaf if you cbb to get BP for Seed Bomb. Alternatively, slap a special move like Energy Ball but you won't get benefit from the Atk boost.
Crobat
• Cross Poison
• Wing Attack/Aerial Ace
• Dark Pulse
• Heat Wave/Return/Steel Wing
Eh. You could keep Fly for in-game purposes > Wing Attack I guess. Last two moves mainly for coverage. Heat Wave is amazing if you can get it, otherwise just Return or Steel Wing. You might also want to consider U-Turn.
Steelix
• Stone Edge
• Earthquake
• Fire Fang
• Crunch/Iron Head/Gyro Ball
Last move is really a filler. Iron Head is a tutor move, so you can opt Gyro Ball and give him an Iron Ball to hold. I guess you could also use Rock Polish as the last move, if you really want a fast Steelix. Or Strength, if you cbb to keep an HM Pokemon.
Give Lanturn Thunder Wave or Toxic for some support, or Signal Beam if you just want an offensive Lanturn.