Animations fails when i add new skinned mesh

I have a prefab with the hierarchy showed in the picture attached.i export it as fbx and add a mesh (named fort in picture) in the project with blender. then I parent the mesh to Hips_int and I attach a armature modifier to the mesh. the root of the armature modifier is Hips_int. I then import it on unity and the animation that used to work doesn't.How can I add skinned meshes without affecting the animation? can I do it unity(when I add skinned mesh renderer component I am not allowed to resize)?

note: my aim is to have multiple skinned meshes so that I can have a customizable character.