Who are the characters in the Audience?
Yes, these are from what I can tell, all servants from Grand/Order.

The Sakura you're talking about in the first image is actually BB, she's just wearing her nurse dress after her Noble Phantasm animation.

In order from left to right, top to bottom, these would be:


BB
Sakata Kintoki 
Medusa 
Osakabe-hime
Henry Jekyll
This one's hard to tell. Could be Okita Alter.
Hans
James Moriarty
El-Melloi II / Zhuge Liang


In the back it gets a bit harder, but again from left to right:


Paul Bunyan
Yan Qing
MHX Alter
Stheno / Euryale
Shuten-Douji
Maybe some incarnation of Gilgamesh


I won't try with the row in front with that image since it's probably tougher... but as a bonus, the one with the spiky crown in front of Shuten is probably Ishtar.