Hi Yquilla;
Diablo himself – the purple-clab figure with the white sombrero – is from Grenadier's 'Western Gunfighters' boxed set. (Now available from Mirliton.) For my money, the nicest set of Old West sculpts ever made.
The big hombre in the peon pyjamas is from eM-4's pre-painted range. A real bargain for what you get, but they're big figures, as you can see. They fit with the Grenadier/Mirliton, and maybe Black Scorpion.
The rank-and-file are a mix of Dixons, SHQ, and Old Glory's 'Warpaint' range. (that's the western range from their historical catalogue, as opposed to their 'Cowboy Wars' figures.)
They all fit together very well. The Dixons figures are better sculpts, and far and away the best in terms of casting quality.
The SHQ are a little smaller, and not quite as good, but still nice. For some reason, it's an often-overlooked range.
The OG 'Warpaint' figures I bought were not much good, I'm afraid. Some castings were unusable. (4th in line in the pic above had to have his gunhand replaced.)
But they're currently being remodelled, so might be worth a try in future.
Lastly, one of the poncho-clad bandidos is from Warrior Miniatures/Over the Wires' 'Wanted: Dead or Alive' skirmish set.
These are nice, chunky, characterful figures. (Avoid the expansion pack, though. It comes with some truly wretched figures in a very different style.)
Hope that helps!