Would this ability stack if i use multiple ringwraiths (rule of 3 of course)? It seems like it would.

i think it definitely woudl.

Each character's power will activate on its own, yes. Ringwraith #1 (and its special power) doesn't particular care what Ringwraith #2, 3, 4, etc (and their special powers) are doing.

so they would get +3 to their defense value if they are arranged correctly?

i was unsure last night when using them so i just went with +1 since it sounded a bit absurd but it felt like it made sense

You clearly haven't seen a team on nine One Of The Nines, huh?

KO one of them, the rest heal all 9 damage each. (The next one KOed heals the rest 8 each, and so on.)

Ugh, sounds awesomely cool !?!

If I get at least 7 of them, though, I would need to find a Jeri Ryan sculpt for the 7th

You could always put a Voyager sculpt on it...

...but that might cause some people to shun you...

UGH! I faced a few of these in a know the other day! TERRIFING!

I felt just like the Hobbits!