Removing glue from Lego bricks
Tough job.
You can try using some nail polish remover to try to start breaking down the glue.
From Removing Super Glue, which they give for advice for people that accidentally glue their fingers together, this procedure might also work for the bricks.

...even though Super Glue is incredibly strong, it has one weakness: acetone.
Acetone is often found in household nail polish remover, and a small amount on the end of a Q-tip or cotton swab applied directly to the glue should dissolve the bond without damaging the skin.

A lot will depend obviously on how much glue was used inside the bricks, but perhaps a little crack and a small screw driver to help pry them apart and keep applying the acetone to the reachable edges can help break them apart.
I don't know if acetone will do something to the brick's color or structure, so proceed carefully.
Good luck.