Everyone is in the throne room.
Sonic, Merlina, Bro, Kiran, Gawain, Tony, Shantae, Yang, Ruby, Sam, Raiden, Snake, SG-1 and Sans.
I went back to your post, and honestly, I don't really think Sans is all too worried about Yang and Ruby. He understands Yang is more than capable of handling herself, and like Merlina, he's noticed that Cal is a potentially threat. More so than Sam, so once Bro and Kiran snuck out, Sans decided to follow and get some answers surrounding Lil' Cal.
Also, Negan and Drax are about to arrive at the throne room.