They decided "Screw the establishment", and started misbehaving. They offed several of the mid-range criminal leaders and started setting up their own organisation...
That's the life and way of crime alright.
It ended in death and, not surprisingly, dishonour.
And that's the way it ends...
I can tell ya though Joe about an interesting case I worked one time that might let your boys operate the way you envision for the moderately long term without getting their throats slit by the locals (the organized, long-term gangs), or having to become part of the locals.
I worked a case against a gypsy organization (floaters). They came in every year, around the holidays, picked some careful targets, people who supposedly were small business owners and had goods stashed on property. Maybe in home safes. They committed armed home invasions, and every time they struck they got a little more violent (the same old story). They'd hit two or three homes a year and we pulled in some of the hangers on, but the evidence showed they weren't locals (they were far too smart to hit in their own neighborhoods, or even their own cities).
They were however highly organized, masks, equipment, careful surveillance of targets before they struck, picking older and more established people, hitting around the time neighbors were away with family or friends. Had a complicated and involved scouting, lookout, and communications system. And I always suspected an incredibly good Intel ring and fencing system, though the fencing system was necessarily local.
By their last attack and home invasion they had gang raped a couple of girls who were unlucky enough to be home from college for the holidays. Like all criminals they eventually "worked their way up to the real stuff," in their own minds at least. Came awful close to taking them apart, even got one assistant by FLIR helicopter and drug him down. But the mains absconded.
That was the last year they struck where I was working. Next year nothing. The case dried up eventually and I never really knew what happened to them but I can make these guesses based on prior experience. 1. The group fell apart. one or more members became continuously more and more violent and it scared or ticked off the others. They split and the violent one or ones probably ended up working independently. The other, or others, went cold. 2. They fell afoul of their network, Intel, fencing, or whoever was helping them. And those guys cleared them out once word about their methods got back around to them. 3. They ticked off the wrong set of criminals and they killed them. 4. They picked the wrong target and got arrested, or injured, or killed by their potential victims. 5. They were taken by the Feds or an interstate task force for operating elsewhere. 6. They got taken for unrelated crimes and ended up serving for that, and are still in, broken up, or never again hit their stride. 7. They could have also just retired, but it ain't likely. Once fellas take to beating hostages and raping little girls, they're too far gone to think about early retirement.
In any case they were moderately successful for two years, in my jurisdiction anyway. By criminal standards. But they had to keep moving, they did not operate on home turf, and they were highly organized, if ever more progressively violent - and that, I'm sure, led to their downfall.
Anywho guys like that could operate successfully for awhile.
Don't be surprised though if your players, or your partners if you're thinking about playing in such a group, suddenly decide that petty theft isn't such a great life and want to make the big score with progressively more violent tactics. That's just the way such things operate. Somebody always wants a bigger thrill, a bigger risk, and a bigger take, come hell or high-water, and no matter how they get there.