In one crawler, you can have multiple actions, and you can have a different indexName for each action if needed. You can also use the parameter pathsToMatch in that action to specify the webpages you want to limit. This will add the records you add in your action to separate indices.
You can use the common domain as the StartUrls, or if needed the set of entry points.
We recommend reviewing this guide for more insight on how to configure your StartUrls.
