Hey!
You can create either few selectors to pick data according to a website, or merge them into each other, but separated by a comma to save space in end results.
Example:
Selector 1 - will pick field named, for ex. Name, on first website, but will return 'null' on second website
Selector 2 - will pick field named, for ex. surname, on second website, but will return 'null' on first website
You can create a mixed selector, with both Selector 1 and Selector 2 inside, but separated by a comma, so it will pick 1st available field. That means, if you reach website 2 and, if two selectors were there, 1st would return null, but instead it will just skip non-existent field and pick second, thus rendering end results much more usable.
As for different websites, you can add any in your Metadata. (Menu -> Sitemap -> Metadata)