Many service providers on AirGigs offer services on a work for hire / royalty free basis.
While we cannot offer legal advice, many AirGigs buyers who plan to release their tracks commercially require "work for hire" contracts from the musicians they work with. You can contact any musician on the platform before ordering, provide project details, explain your requirements and upload your contract.
A quick Google search will provide many work for hire contract resources that you can have tailored to your needs.
For more information, visit our terms "COPYRIGHT OWNERSHIP AND LIMITATIONS"