@Bharath- Bharath-
Phase-1
First Identify the Backend DBS to migrate.
How are the tables in each Backend DB created.
Are they one time creation or are imported on monthly bases.
Phase-2
Tools Needed - SQL Server , SSMA for raw migration of the Backend DB.
SSIS if the tables are created from the flatfiles.
Use SSMA manily for getting the Data Dictionary.
Then recreate the tables in the Dev environment.
Coming to queries. In MS Access they are jet based. You need to rewrite them in T-SQL. This is quite easy task if you are having good/moderate knowledge in SQL.
Create the queries of Access as Views and link them to the FrontEnd.
The main thing here is you have to make a plan and then approach each time you face a problem. There are lot of forums and people ready to help. This is how IT knowledge has grown. So let us know more information.