Armature issue with Blender import

Enclosed in the attached Blender file is a mesh/armature setup I'm using for a project. The problem is centered on the two doors in the mesh, Ovi1 and Ovi2, and their associated armatures, Kahva1, Kahva2, Sarana1, and Sarana2. Kahva1 and Kahva2 are bound to the handles of each door by using vertex groups and control their turning, ans Sarana1 and Sarana2 are attached to the doors themselves with the same method to simulate door hinges. In Blender, the armatures function as intended; the doors turn on the hinge armatures, handles and all, and the handles turn independently when the handle armatures are manipulated. When exporting the meshes and armatures involved to Unity, however, the handle armatures don't turn the handles (or anything at all), while the hinge armatures function normally. What could be causing this issue?

 

I haven't modified to make it work in unity but I think the problem is you can only have one armature modifier per object.

Also usually I only have 1 armature per scene with all the bones attached to it (usually to a root bone), although I suppose it might work with multiple armatures. I never use the vertex groups function at the bottom of the armature modifier so this might be causing you problems too.