To explain the tiers
Drifter is Drifter and planning on jumping his teammates.
Silver and Venator flat out told Drifter he dies tonight.
Shiv threatened to murder him but didn't explicitly say he was... but also is 100% going to try and kill Drifter. Killing him is probably one of the biggest things to cement his redemption. Grey Talon is pretty busy but also 100% will try and help, while Haze likely has a kill order on Drifter and unlike Seven, theres no need for a truce. Warden probably will go to hunting monsters like Drifter when the Patrons are defeated, and Holliday has a strong sense of justice and zero survival instincts.
For might, these are either people Drifter has explicitly threatened what they care about (The Baroness, Ambassador Nashala, Miss Shelly), might just oppose him because he's the fucking Drifter and a threat to what they care for (Rat King, Baba, Abrams, Solomon), have an ego large enough they will fight him (Apollo, Yamato (Who also benefits from a legitimacy bonus if she kills him)) or in Calicos case, might genuinely just get paid to kill Drifter. Maybe by Doorman or Nashala.
For if they see others doing it, these are characters who wouldn't do it unless they feel they might win (Infernus and Celeste both have to much of a survival instict to kill him, but also might join in if they see the 7 guys going to kill because Celeste literally is gonna get hunted by him, and Infernus won't want him to target Jezibels.) Ivy I feel won't think of Jumping Drifter do to... well her naivety, but I doubt she has issues killing him if she knows what he does. Vindicta wouldn't care unless Wesley asks, and since Grey Talon is the person she cares the most about she might go and help, while Mina it's entirely politics: If she wins and she kills Drifter for violating the Venery (Before she can remove it) then that's a massive legitimacy boost, if she loses then Simon will probably not be able to retaliate against her as easilly for her attempted coup since she did just help kill Drifter.
Finally, I feel Vyper would see what looks like a gang mugging someone and decide 'Yeah ok' before running up to shank the victim. I don't even think she'd realize it's Drifter, just pure animal instincts as a bottom feeder.