I have a basic hinged object that is comprised of two halves, and opens like a clamshell. What is the correct way to export this to Unreal, with LODs? Is it better to export the object as an FBX with LODs and armatures, or just export the two halves as separate objects and combine them in a blueprin…

Yes, possibly 3 if you have a static pin as part of a hinge and you need that sort of detail. Overall, less is best (so you’d merge the pin too).