@vinay p
Try with CountText,CalculateRecordStats processors will gives what you are looking for.
To get one summary flowfile from 3 flowfiles then first you should merge 3 flowfilee into one by using MergeRecord/MergeContent processor then use CountText,CalculateRecordStats processors to get the summary of the flowfile.
Then use PutEmail processor to send to send the flowfile as an attachment.