2.Center of the Photo, the Green mat colonial tunicate (MantelDieren)
ay be Trididemnum miniatum, which forms "white to emerald or lime green" cushions (size to 1 cm)
The Australian Ascidiacea, Part 4:
https://www.biodiversitylibrary.org/page/40460926#page/273/mode/1up

https://old.observation.org/waarneming/view/180811964

Can you tell me

1. Sea Squirt Class Ascidiacea Zakpijpen
   https://www.inaturalist.org/observations/34031818
   https://old.observation.org/waarneming/view/180811964
   Green Sea Squirt (Didemnum molle), colony, corals, Bali, Lesser Sunda Islands, Bali Sea, Indonesia, Indian Ocean, Asia

2.Center of the Photo, the Green mat colonial tunicate (MantelDieren)
I am pretty certain they are in Didemnidae, as they share a common cloacal aperture as you say, but the branchial siphons (the small inhalant ones) do not seem to be in circular or linear systems. It is also more or less encrusting. As for this particular species, I've never seen it before.
A quick search suggests this may be Trididemnum miniatum, which forms "white to emerald or lime green" cushions (size to 1 cm)
The Australian Ascidiacea, Part 4:
https://www.biodiversitylibrary.org/page/40460926#page/273/mode/1up
Possible Image (B)
https://zookeys.pensoft.net/showimg.php?filename=oo_30408.jpg