TLDR: I've lost 3 Firefish, a Clown Goby, and a juvenile Clownfish. Aggressive Clown and Serpent Star are gone.
My LFS (who also helps service the tank) said the large female Clownfish is very aggressive, which I certainly agree with. She said it looks like she's defending a clutch of eggs and was not at all suspicious of the Serpent Star. She said stress from the bullying could be causing the lower, more timid dwellers to starve. I upped feeding since water parameters are great, Spot fed the Star and added pellets for him to scavenge. I since lost the Clown Goby AND juvenile Clownfish.
I re-homed Mrs Bossy. The serpent star can be attributed to all, but the Clownfish seemed to not fit his profile. This week I got #3 Purple Firefish along with #2 Clown Goby, and the kiddo was quite fond of a Royal Gramma. The Firefish didn't last the night.
I'm 99% sure that the serpent star is hunting and becoming very good. The Gramma claimed a little cave under a rock overhang. This morning the Star was using his body to form a third wall to seemingly make it a trap. I zipped up to the LFS with Serpent Star in tow and came back with #4 Purple Firefish. I figure I can also attribute the Clownfish to him if he was "evicted" by Mrs Bossy and became more vulnerable.
If this Firefish doesn't make it, I think I'll be done with them. I'm not too suspicious of the CBS as it seems that the fish that have gone missing are far too large for him to overpower (several times his weight)... even if he had plenty of time getting a propper grip. And I really like him.
I plan to get some new clowns once these folks settle in. Leaning toward Frostbite and Midnight (complete opposites

).
In good news, my Kenya Coral is flourishing so well that it's almost too big. A second one popped up on a rock and is now big enough to be a centerpiece on its own!!