I don't have any experience in this area, but I see very little useful relevant information outside of the user guide and the source code. Maybe somebody with more experience will respond...
I think the one tricky thing is that you need to immediately terminate the process when anyone DENIES. This could be done easily with a custom TaskControllerHandler, I think. The rest seems like straight JPDL.
You could also try to:
- Create a custom decisionnode that creates enough tasks (see the wiki for an example)
- Use an actionhandler on each 'deny' transition that cancels the parallel active tasks and sets a processvariable.