1. How to set the variables in the rule task node(drl file) and carry the same variables to further nodes.
you could try something like this:
when
$process : WorkflowProcessInstance()
then
$process.setVariable("name", "value")
2. is it posssible to fire the drl file or rules by sending the drl file name as a parameter to a node as on-entry condition.
Why would you like to do that? In my opinion for such purpose you have bunsiness rule task
HTH