Based on my experience you will need to have people who knows how to use java to build applications.
The jBPM project uses standard technologies in the java space to work. So your devs will need to be familiar with Hibernate/JPA for example. Spring is not a requirement but you can use it if you want.
Your devs will need to know how to set up a database and how to add a library (the jbpm lib and all its dependencies to your project).
If your devs have those skills, then you will need at least one person which understand the BPM concepts and why you are planning to adopt BPM.
The same for the Rule Engine, you will need at least one person which understand how Rule Engines usually work and how to use it.
The rest is pure Java.
Cheers