After a lot of googling most things that comes up are outdated. Tilt brush now has its own .fbx export. It also comes with a JSON file which I assume is for the colors. I can import everything but the JSON in to my unreal project. When it comes to the JSON it crashes. If I skip it then my tilt brush drawing doesn’t have any colors.
In all honesty I’ve tried tilt-brush to unreal as well. The only thing i could manage to get it to do well was take my initial models.
This isn’t really much of the answer your looking for. But my advice is to export it to a program that will take everything tiltbrush uses, then export it to unreal from that program. If you figure this out, i’d love to know what you did.