If you can get all the process ids, you could send the signal one by one.
Also, i apparently fix the problem changing the class org.jbpm.bpmn2.xml.IntermediateCatchEventHandler. In contrast with the class org.jbpm.bpmn2.xml.BoundaryEventHandler, the methods handleMessageNode and handleSignalNode dont set the scope of the node to "esternal". I added the line eventNode.setScope("external") just like it was on org.jbpm.bpmn2.xml.BoundaryEventHandle in both metods and the test case described before star working.

-Using eclipse Bpmn2 diagram editor (inluded in jboss developer studio jbpm plugin) create a simple process that contains some messages and signals on it. In my case it was a start node followed by a parallel gateway with 3 outgoing events (one message and to signals, both signals with the same type) and each event was followed but different Human tasks so i can check if the events were triggered.
-Create a RuntimeEnvironmentBuilder builder:
RuntimeEnvironmentBuilder builder= RuntimeEnvironmentBuilder.Factory.get().newDefaultBuilder()
.entityManagerFactory(emf);
builder.persistence(true);
builder.addEnvironmentEntry(EnvironmentName.TRANSACTION_MANAGER,
tm);

-Register the process:
builder.addAsset(org.kie.internal.io.ResourceFactory
.newClassPathResource(processDefName), ResourceType.BPMN2);

-Create a signleton RuntimeManager:
RuntimeEnvironment environment = builder.get();
RuntimeManager manager = RuntimeManagerFactory.Factory.get()
.newSingletonRuntimeManager(environment);

-Get session:
KieSession session=manager.getRuntimeEngine(EmptyContext.get())
.getKieSession();
-Start process:
Long id=session.startProcess(processId, params);
-Send a message then a signal
session.signalEvent(messageName, message,id);
session.signalEvent(signalName, signal);
After this, if i check the created tasks there is only 1 created and should be 3.
-In contrast, if i change the second line from session.signalEvent(signalName, signal);
to
session.signalEvent(signalName, signal,id);
now there are 3 human task created.
-Same thing happens if i rebuild the manager before the signal:
manager.close();
manager= RuntimeManagerFactory.Factory.get()
.newSingletonRuntimeManager(environment);
session=manager.getRuntimeEngine(EmptyContext.get())
.getKieSession();
session.signalEvent(signalName, signal);
After this the 3 tasks are created correctly.