Question

1)What's the difference?
2)What Tier are they?
3)Can they be put to use?
4)What is a good moveset for both?

Answer 1

• The difference is that Illumise can only be Female while Volbeat can only be Male.
• They are both in the NU tier.
• Depends what you mean by put to use, as in what kind of use? (By the way, both do not learn ANY HMs at all.)
• As for movesets:
  
  
  • Volbeat: http://pokemondb.net/pokebase/5240/what-is-a-good-moveset-for-volbeat
  • Illumise: http://pokemondb.net/pokebase/5276/what-is-a-good-moveset-for-illumise

Have fun ~