How can we achive the replica of databases for SQL Server?
To reinforce what Jon says - a single DB to which all clients connect all the time, with the schema designed accordingly, will be a much better solution.  You only need replication in a few circumstances.  One is if a client machine must be able to work while disconnected.  Another will be if there are huge latency issues between your various sites.  Replication, especially two-way merge replication, can be a huge pain - during upgrades, for example.