There could be two ways,
1- Freeze any changes to the two servers and migrate all contents/sites to a single server.
a- You can do it using bulk export and bulk import
b- You can also use acp based export and import site/content tool.
Upto 5.1 , maywork for 5.2 as well: https://github.com/abhinavmishra14/alfresco-share-import-export/tree/master
Upgraded to SDK 4.1: https://github.com/abhinavmishra14/alfresco-share-import-export/tree/sdk4.1
c- You can also use this script:
2- Make use of replication, once all three servers are in sync, close down the 2 you don't want.
(ACSCE, AWS SAA, Azure Admin)