I always zero out my location coordinates in Unreal when I import an object. Essentially, if everything is coming from the same 3DS model, when you import your walls into Unreal, change the transform location to 0,0,0. That puts the origin from the 3DS model at 0,0,0. Then when you import your door frame from the same 3DS model into Unreal, set that object’s transform location to 0,0,0.