What happened to the other Eternian Astrisk Users?
Unmarked spoilers for Bravely Default and Bravely Second below.

Not accounting for the alternate reality versions, of which there are several for each character, this is the status of each of the listed characters by the time of Bravely Second:


Victor S. Court - killed by the party in Eternian Central Command back in Bravely Default (you listed Vincent S. Court, which is actually Victor's father. Vincent was killed by Victoria before the events of Bravely Default)
Victoria F. Stein - killed by the party in Eternian Central Command back in Bravely Default, along with Victor.
Sage Yulyana - killed in the battle with the Ba'al, Diamante. He managed to seal Diamante into the Kustra Archipelago before he died.
Lester DeRosso - disappeared from Luxendarc. This one is slightly more vague. The DeRosso we see sacrifice himself against Ouroboros in Bravely Default is the one from that "final world" and not from the original world that the characters originate from. After the events of Bravely Default, the original DeRosso helped Yulyana hide the weapons that Yulyana had previously stolen from the Crystal Orthodoxy (the OP weapons in the blue chests, if you played the game) in small pocket dimensions under Centro Keep and Mount Karka. He vanished after that, no longer being found in Vampire Castle (occupied by Yōko) nor anywhere else in Luxendarc.
Qada - killed by Kamiizumi. He intended to overthrow the Duchy after being defeated by the party in Bravely Default, but was overheard and struck down by Kamiizumi. According to the wiki, his ghost remained there, and was unaware that he had been killed.