I highly suggest using Artemis for this achievement in a game type like Joust or Arena, where you can always guarantee enemies are going to be in close proximity to one another.
Artemis is extremely powerful even when not built correctly, but with the proper items such as Rage, Titan's Bane, Devourer's Gauntlet, The Executioner etc she becomes an absolute NIGHTMARE for opponents.
In addition, Artemis'
ability, Vengeful Assault is a buff which increases her movement/attack speed for up to 5 seconds when maxed. As this is a BUFF, using her bow as a ranged weapon basic attack will still count for the achievement. All you need for this is to kill two enemy gods within 4 seconds of each-other.
You can also get Artemis for FREE if you don't have her using the promotion on the official Smite Twitter account @smitegame. Check it out at
https://twitter.com/SmiteGame, the link to the free Stalker skin (which will also unlock Artemis for free) is in their profile.
Finally, here is a resource from Tiermonster, the EXCELLENT Smite reference guide which I feel everyone playing this game should check out:
http://tiermonster.com/god/7/artemisGood luck!