As far as i know(and FAQ states) you dont pay any royalties for movies made with UE4.
Are any revenue sources royalty-free?
Yes! The following revenue sources are royalty-free:
Ancillary products, including t-shirts, CDs, plushies, action figures and books. The exception is items with embedded data or information, such as QR codes, that affect the operation of the product.
Consulting and work-for-hire services using the engine. This applies to architects using the engine to create visualizations as well as consultants receiving a development fee.
Non-interactive linear media, including movies, animated films and cartoons distributed as video.
Amusement park rides and live installations.
Truly free games and apps (with no associated revenue).