My take is that Ardos and Eldes - yes, both of them - are far less popular among Cipher people than one would perhaps assume.
Disregarding the additional nuances of Ardos probably losing more likeability points due to being an asshole and Eldes winning some back by being nice, the main thing about them is that they are the Grand Master's sons and get special privilege and treatment for that all the time, even compared to the other admins who are of the same rank. This gets especially egregious when they get that over Nascour who is not only Chief Admin/Executive ranked above the admins but also a relative of theirs in my verse (context). And yes, you bet that this pisses him off, creates interfamilial conflict and is used by him to do some campaigning and alliance forging behind the scenes.
In addition to that, a lot of members of Cipher are actual, hardened criminals (from the thugs Cipher hires on the side to the more sophisticated and sneaky conpeople and killers in its upper ranks) and can tell that Ardos and Eldes got their ranks and privileges purely by being born in the right bed. They are strong Trainers, that is something people will concede, but that's also about it.
They suck at crime and lack experience in the actual criminal scene. They could not pick a lock if they tried. They know very little of the daily dealings of the gangs and current state of affairs. They can defend themselves and put people in their place if they have to, but the gang leaders don't respect them (meanwhile compare how Nascour made Gonzap his little bitch)
Most of their time is spent hanging out with their father and traveling. Ardos and Eldes do very, very little of the actual work that goes into building up and running the syndicate - no research, no lab work, no recruiting, no participation in gang wars or street fights, no coordinating or overseeing anything or anyone, etc
Also let's be real: Greevil can absolutely defend himself and he will. He doesn't need them, it's mostly for show and convenience
In addition to the combination of 1) "people can tell they aren't proper criminals" plus 2) favoritism from the Grand Master plus 3) their own family member, Chief Admin and the one among the Cipher bosses who is the most directly involved with everyone else (I tend to say that Nascour being a decoy boss means he still counts as a boss) making sure to remind everyone of these facts and undermining the standing of various Verichs in his own favor, there is yet another factor. Many members of Cipher are, if the general state of Orre is anything to go by, poor. We even have at least one confirmed working class person among the admins. And these people have yet another - very good! - reason not to like Ardos and Eldes. Maybe they can respect Greevil a bit more because he actually ran (and still to a degree runs) his business, but his boys? They were just born into luxury, they did nothing to earn this.
I imagine that, even when other Cipher members hide their feelings - which I imagine they don't often do, at least not the higher-ups - the brothers are aware of this. Eldes deals with this by keeping his head down, smiling through snide remarks and potshots aimed at him and just trying to be nice and pleasant, which some people appreciate on an individual level and sometimes has them go as far as to say something along the lines of, "well, at least he's alright", but others interpret this as yet more weakness on his part, lowering their opinion of him even further. Ardos fights fire with fire - he gets smug, snaps back, puts people down, holds his power and money over their heads and forces compliance, if necessary with literal fire from the maw of dragon Pokémon. His credo is: "If you hate me, fuck you, you filthy little peasant".