Legal - How to allow modders to use my tools that are dependent on licensed assets?

I am making a moddable game. I have working system for serializing/deserializing items etc. For purpose of easy item creation in unity I made editor windows that help you with process of creating objects and setting their properties. The thing is these windows are dependent Odin Inspector and Serializer. My question is how to let modders create their own items with those editor windows? I wanted to make project open source (so they can put it in Unity and just do it as I did) but obviously I can't put licensed files there.

 

I imagine you'd either need to reach an agreement with Sirenix or have each modder purchase a license.