I guess you may use RabbitMQ or any other brokers. It will act as like a "trigger" that will tell "Hey Website B, Website A just updated itself, check it out".
Add a "API" route that will bring you data to import and you're right : Once a website is updated, others will know and will be able to get the latest revision.
My advice with those "auto nodes ...
Assuming your souce class works, there are two things I'm spotting:
Do not prefill internal entity keys like nid, uuid or revision_id in the migration YML, the Migrate module will set them for you. Manually setting them is not required at best, and a potential source of errors at worst.
If your text fields are plain text fields, then your YML should ...
First of all, you only need two yaml files, one for the default language and one for the translations.
If you are migrating for example a content type of bundle pages and your default language migration is eg. my_website_migrate_node_page, then in the my_website_migrate_node_page_translation define your dependencies as follows