I am not a lawyer, and interpreting legal documents can be tricky. When in doubt you should always consult a lawyer about your specific scenarios.
That said, these things are usually covered in the EULAs for the software or services in question. They are generally completely independent of eachother.
Unity's EULA is here. The relevant two passages are:
a Commercial Entity that has either: (a) reached annual gross revenues
in excess of US$100,000, or (b) raised funds (including but not
limited to crowdfunding) in excess of US$100,000, in each case during
the most recently completed fiscal year;
an individual (not acting on behalf of a Legal Entity) or a Sole
Proprietor that has reached annual gross revenues in excess of
US$100,000 from its use of the Unity Software during the most recently
completed fiscal year, which does not include any income earned by
that individual which is unrelated to its use of the Unity Software.
These are describing the conditions under which you cannot use Unity Personal any longer. Basically, once you make $100,000 in annual gross revenue, or get external funding (from investors, Kickstarter, et cetera) for an equivalent amount, you must purchase a Unity Pro license.
Facebook's platform policy is here. You may publish to it and use its APIs for free, although you read that entire document and be aware of what you're exchanging for "free" (especially the parts about how they can analyze your app and traffic for any purposes, et cetera). They do not promise the platform will always be free:
- We don’t guarantee that Platform will always be free.
You also have API limits you have to confine yourself to:
- If you exceed 5M MAU, 100M API calls per day, or 50M impressions per day, you may be subject to additional terms.
These terms are not spelled out; that usually means that if you exceed these limits, a representative from Facebook will contact you and you will have to work out a private legal agreement between the two of you that defines you terms (including any payments you may need to make) in terms of your API usage volume.
You're probably not going to hit those limitations at this point in your career, so usage of the platform is effectively free, unless you are using their payments APIs (for e.g., microtransactions). Those are a separate service, and using them involves a 30% cut that Facebook reserves for itself.
Other than that, you are free to use your revenue however you see fit; it's yours.