They are not

Again this is the Holy Knights history:
Sommers v Gaban - Pretty much a one shot
Sommers v Ray - Got oneshot
Newgate vs Maffey - trash treatment (Newgate didn't even acknowledge her as an opponent)
Xebec v Garling - pretty much negg’d and off panel to boot even with Imu’s buffs & a Domi reversi army for support.
Then there’s Gaban’s statement on how the Roger Pirates packed them up each time the Holy Knights challenged them and also the CoC angle which makes any one of them without it fodder for the most part against competent CoC users.
Keep in mind again that Gaban scolded Zoro this arc to raise his standard in order to be able to support Luffy. Imagine him getting matched up against these bums after that statement. IMO not gonna happen.
holy knights are Imu’s mid tiers so they are gonna be opponents for the mid trio bar shamrock imo.
only characters of relevance imo are Dorry & Broggy & Imuko with the exception of backup coming from Marijoea.
With regards to Brook, I don’t really see him doing anything of relevance to Imuko combat wise but he well get his moment. Gunko prolly dies like Harald did