I have concluded my investigation on the spawn grief, using assets I already had, and a LogBlock result that I stumbled upon purely by chance.
Basically, Soccerkid255 did, from what I can tell, MOST of the damage. UnicornFish is only responsible for the destruction of the Piston Moving Pieces, used as the "invisible blocks" to hold back the water. Here are evidence pictures:
Soccerkid255:
UnicornFish (look at the circled text):
All of the damage has been repaired so far. Based on the nature of their offences, I have made the following conclusions:
UnicornFish: I'd say we let it slide. Uni's never griefed before, and it wasn't TOO big. I think we can continue to trust Uni, so long as it doesn't happen again.
Soccerkid255: Based on how MASSIVE his grief was (almost the entire spawn), I think he either deserves a perm ban, or a 1 month ban.
I'll wait for other staff's opinions before I truly pass judgement, though.