There's supposed to be a way to mirror skin weights... I didn't manage to do it first time I tried, but maybe some of the more experienced users can help you with that.

About the scene:
*You don't have to use a translucent material to look through the mash. Use 'Shading > X-Ray' instead. (for a shelf button see FAQs).
*You have some non-manifold geometry in the lags. Look from inside the model and delete the unneeded faces in the legs.
*delete history from time to time (where you don't need it) ('Edit > Delete by type > History' while selecting an object).
While investigating the mouse it often did some freaky stuff... It may also be the version (I have 8.5).
*I'd soften many/all of the edges ('Normals > Soften Edge' while selecting it).
*EDIT: Beware - this may un-skin the mash. Always make sure you're done with the model before skinning it
Benny