So you are trying to merge bones together?
In that case, you must do everything manually.
At least in my experience with Blender, you cannot copy the weight of a bone onto another. I have not found a script for it (although it would be immensely useful. The reason being that many times bones share the same vertices, and copying the weights from one onto another can cause conflicts.
At this point if you want to copy the bone weights, you have to do it all manually. That means weighing each vertex point by point and combining the weight values of the two bones.
So for example, if bone 1 has a weight of .25 on vertex 7, and bone 2 has a weight of .5 on the same vertex, then the merged bone would have a weight of 0.75. You will have to do this for each individual vertex, and so on...