Hi Felix,
The jBPM-4.3 already support drools integartion. You could use RulesActivity directly.
If you want to let all the child executions of a forkActivity running parallel, you could set continue attribute like below:
<fork>
<transition name="A" to="A"/>
<transition name="B" to="B"/>
</fork>
<java name="A" continue="async"/>
<java name="B" continue="async"/>