Hi Abhishek,
Please don't use duplicated jbpm.tx.***.cfg.xml at the same time. If you want to run jbpm4 in the jta environment, you should delete jbpm.tx.hibernate.cfg.xml.
But here is still a possible bug for jta configuration, so if you meet an exception like 'cannot lookup UserTransaction from jndi', please refer this issue.
https://jira.jboss.org/browse/JBPM-2694
Matin has already provide a patch for this scenario, but I am not familiar with weblogic, so I can't tell you whether it will effect your work. And good luck. :)