No, we have procured aem assets and are planning to host it as a standalone asset repository. So AEM Assets author (& publisher too) is server on its own. we have different sites instances for various applications.
Note : I am not in a position to change this architecture of having different assets and sites instances. I am looking at a viable solution to have the approved content from assets to be made available to my applications hosted in aem sites.
You can setup a separate replication agent for the sites author instance and replicate assets. Refer How to Replicate Using Specific replication Agents. For the second requirement also you can setup a separate replication agent to replicate content fragments and leverage content services to expose the content.