Hi Peter and welcome to the RH forums.
Let me answer your first question by stating what is part of each Robohelp licence. It is in fact more than just RoboHelp but a suite of products called RoboHelp Office that includes RoboHelp HTML. This allows you to create web based output as well as others, for example a Word or PDF file. RoboHelp Office also includes an application called RoboSourceControl which allows multiple users to work alongside each other by checking topics in and out. So RoboHelp can do exactly what you require. Robohelp Server is a completely difference beast with a very different purpose but this is not what you want. You can read more about this here and here.
As for licences, you'll need a RoboHelp licence for each user. I am not an expert in translation but there are others on these forums that are. The general premise seems to be send the translator the project files and they send them back. You'd just need to unsure the translated files are used when creating the output.
The RoboColum(n) @robocolumn Colum McAndrew
Thank you for your explanation, it clears up a lot of issues I've been having with the research!
However, I can not seem to locate the aformentioned Robohelp Office on the Adobe pages anywhere, is it just an unofficial name for Robohelp 8 (meaning that when buying a copy of Robohelp 8, it includes the HTML version and RoboSourceControl)?