Based on what you are describing, one way to solve your issue is to use hidden fields.
When you are creating your form add a few extra hidden fields to it like: utm_campaign , utm_source , utm_medium or the less common ones like utm_term & utm_content.
After that, every time you are setting up a different Facebook ad and/or campaign make sure you update the URL you’ll be using for the ad accordingly.
Ad I: https://www.awesome.domain/?utm_campaign=leads&utm_source=facebook&utm_medium=ppc&utm_term=cars&utm_content=red
The Unbounce page and form will automatically pick up the UTM tags so when a lead does come in, you’ll be able to tell if it was from the ‘red’ or from the ‘green’ ad/campaign as per the example above.
You’ll also have the added benefit of being able to break down these results in Google Analytics for post campaign analysis.