doubts in assembly

Hi all

my previous questions on mapping are still pending and now i have a new set of questions on assembly

If i am using read information from three  different sources: one from inhouse sequencing method, one from downloaded reads information and other from a database of ESTs.

1. How do i convert the EST database to a dataset of reads?

2. After assembly, can i say what percentage of the reads assembled are from which data sources?