Hello nupur,
For your First Question answer is: You can do merge forms in two ways. First is Open existing form, Go to File menu and click Merge Forms. Select the form you want to merge and click on “Merge forms”. The data which is merged will be seen in the same form itself. Second is Go to Merge Forms View in your form library. In Merge column in Merge Forms view, select the check box next to each file that you want to merge, and then click Merge Forms. New form will be opened with merged data from files you have selected. These merged forms can be saved or submitted to share point form library. One Important thing is data in repeating sections only will be merged.
Hope this helps!