Alongside Gardevoir and Wigglytuff, another fairy-type Pokémon I would recommend is Togekiss. Although Togepi is difficult to obtain in Hoenn, I believe it would still be able to make a great member. With Serene Grace and Air Slash combination of Togekiss, along with Roost, things will wind up to be a piece of cake for us.
As for ghost-type, I feel Dusknoir would make a nice addition. Its superbly bulky, and could endure ton of hits for you without any trouble at all. Gengar wouldn't be a bad option, either; it's quite powerful on its own, and would have chance to take down a great deal of opposing Pokémon for you.
Good luck, friend!