There are two ways you could go: replication (managed by SQL Server) or change your applications to interact with a middle tier that will perform the updates (and queries) instead of the clients interacting directly with the various database servers.
#1 will require minimal code changes or development time
#2 is (potentially) more robust and scalable for the long term.
To make a recommendation I would need to know a lot more about your application and the databases involved. Also what is your business plan? Growth expectations? Transaction rates? etc. all this needs to be taken into consideration before deciding on a strategy that is optimum for your situation.
The probability of survival is inversely proportional to the angle of arrival.