How do I export character animation with gun static mesh

I have a soldier character I have attached a gun static mesh to the hand joint and in the animation preview the gun moves with the character shooting animation, but it says (preview only) I want to export the character with his gun into Marmoset Toolbag 3 but when I import the fbx the Soldier character shooting animation works but the gun does stays floating in mid air and does not work in conjunction with the kickback firing animation. I can get it to work in UE4 animation preview but when I export the animation fbx the soldier is animated but gun is static, Is there any way to export a fbx with its animations and the additional mesh attached to his hand work work with the animation? instead of just floating in mid air?

There is no way to export out the relationships proprietary to unreal in a way that would work in marmoset that I can think of.

This seems like more of an issue with marmoset, you need to figure out how to attach meshes to bones on skeletal meshes there. (I have not experience with it so i don’t know if that is possible)