My partners and I have been building an application that requires users to authenticate with password and user ID for member registration and transaction. Very often, tasks for designing UI, Datagrid view event trigger and data access using SQL are allocated to different person. Sometimes, there are different versions to be updated but the database structure used are different

If everybody finishes their own part and submit the project on their own onto the shared cloud rivers, there must be a huge cost for software maintenance and re-engineering. How should the task to be submitted so as to minimize the cost for re-engineering without the software like winCVS and Tortoise HG?