MacOS image licensing query for virtual machines (Corporate/Enterprise Use)

Hello all,

I want to create a virtual machine with a MacOS image inside a corporate virtual machine. I am comfortable with an older version of mac too.

I have identified 2 ways i can get macOS in a corporate virtual machine:

1) using an ISO image on a fresh/blank virtual machine

2) using oracle virtual box on windows virtual machine

I want to know 3 things as follows:

1) Is apple macOS ISO images free-to-use or paid/license based?

2) If paid/license based, then at least are older macOS version like Mojave or earlier free-to-use?

3) Oracle virtual box is open source, but does it come with some macOS image by default or do i need to download it from somewhere?