Did a couple of these "courses" when I was at college and Uni and it seems the key thing to have is a clear end goal.
You need to know what they're going to achieve at the end of the week and put them into realistic teams to do it.
You could have each child working on a separate thing but how i've always done similar "courses" is to have one overall project and each individual works either alone or in a group to assemble a section of it, with it coming together as a whole at the end of the week.
If it's a full 5 day thing then it might be worth doing something similar to the below:
Overview of Construct 2 and get everyone to complete a basic "game" in it and then split everyone up into teams for Art, programming, sound, etc.
Not sure if this will be too advanced for 14-15 year olds though, without knowing their backgrounds.