Just a question: In spanish, does the word profesional has two meanings like in english? I explain myself: You can say "They are professional soldiers" meaning that that's what they do for a living, they don't just play soldiers. BUT you can also mean that they are professional in what they do, like: "What if they do a mistake and kill the wrong guy? - Don't worry, they're very professional." In that case, it's more their quality as soldiers than describing their state. Does it work like that in spanish as well?
I think more about full time trrops, like America's army. I would presume that one would refer to mercenaries as "mercenarios" etc. I live in the Dominican Republic now, and the city here seems a good deal more "militarised" than in Anglo-lands. The sight of soldiers or national police forces carrying assault weapons, and private security guards with shotguns, is ubitiquous.
No it wouldn't. A mercenary while paid to do his work which would make him a professional still belongs to no army, has no rank and is subject to other limitations. A security contractor would not be considered a professional soldier as I understand it. Despite having likely once been one. A conscript probably wouldn't either despite earning a salary.
Ustedes doesn't mean “you all". It is the plural form of “you". “You all" is colloquial, but "you" requires neither “all" nor “all of" to be plural in by English. Sometimes “ustedes" is described as “you all" but that is just to avoid misunderstandings due to the ambiguity inherent in having “you" be both singular and plural.
“You are professional soldiers" (no “all") is what this sentence translates to. The absence of “a" and the -s on the end of “soldiers" are more than sufficient to communicate the plurality. “All" would be “todos" and would alter the meaning of this sentence.