I don’t know what you are doing exactly but I can tell you :
In blender when you delete things from an armor and it still imports the same things in the armor the more likely reason is that you may have removed the items on the Pose and not in Edit Mode.
Editmode deletions propagate to pose mode. Vieceversa they do not.
Your animation is likely Baked (that’s usually how blender imports from an FBX, 1 key every frame). Before exporting you need to NLA Bake the action with visual and whatever other options within the panel you think appropriate - Then the files can be re-imported and the armature changes will take place without issue.
For putting the weapon in hand and animating - depending on actual needs (since your need is to spawn via BP you’ll have to work the BP ) - you can try following the sequencer tutorial.
