On my Pally/4x DK team, my Strangulate is set up like this.

I use the Gladius frame to target.
On press 1, DKs 1 and 3 focus that target.
On press 2, DKs 2 and 4 focus that target.

The Strangulate has DKs 1 and 2 cast at focus, on press 1.
And DKs 3 and 4 cast at focus, on press 2.
There's no guarantee they'll be facing their respective targets... but if they are I get two different targets Strangulated and a second use at those same two targets (either later, or right after they trinket).



The biggest trick is going to be setting targets.
If you're not in Arena, you probably don't have a raid frame for opponents.

You can use the addon Battle Ground Targets.
This shows the name and class (class colors too), of everyone on the other side.
It also shows their health, if they're in range.
You can click on their bar to target them.

You could set up a Round-Robin effect to set focus.
And then cast at focus.
Or alternatively, if your effect is a ground target... then scatter where they'll be or broadcast to where they are now.