Re: How Do I Go About...
Hmm...Well, I used the strategy of putting Dusknoir to sleep (with a Sleep Seed-bring a lot), and focusing on the Sableye first. If you have a Vile Seed, that'll be a great help, although you may want to save it for Dialga (c'mon, you already knew you'd have to face him XD).
Once Dusknoir is the only one remaining, turn off all of Eevee's moves except Bite (and maybe Sand-Attack), and make sure "Selected Move User" is on. Basically, let Eevee do all the damage, and you keep his health up with Oran Berries so his Run Away tactic won't activate.
Hope this helps!