I've seen designs using cave spiders where they're funneled into a very small space, with the user hitting the spiders through a small gap in the wall (using something like iron bars), without the spiders being able to retaliate. In order to adapt it to two people (or more, using more forks in the funnels), you could simply have two separate streams of water coming from the spawner (in equal proportion), funneling into the so-called "kill zones" described above.
Private Mod Note
Rollback Post to RevisionRollBack
"I will not waste time trying to make my enemies' deaths look like accidents. After all, I am not accountable to anyone, and my other enemies wouldn't believe it was an accident anyway."