Hi Raghu,
Unfortunately any method to get this information will rely on the team members accurately and consistently recording their work.
Using a custom report is a good option to get the information that is available. Where you are entering the Data in the "I want to see" section I would include:
Sum of Task Estimates
Sum of Task To Do
Sum of Task Actual
Then under the "Broken down by" section I would include:
Work Item Owner
Work Item
Under the Filters section I would add one for Iteration.
This should generate a report that provides estimate for the tasks, the to do remanning, and the actuals if any are entered broken down by the owner and the task name. As I mentioned the available reports can only provide the information that has been entered so if they are not entering information or entering it incorrectly it will affect any report.
It sounds like you are already doing this, but I wanted to go over it in case it helps you or anyone with a similar question. Please let us know if you have any questions.