Sounds like the drums may have seized from behind, especially if the rear brakes haven't been done in a while. You may need a puller---tool with four hooked "arms" and a center bolt... wrap the arms around the edges of the drums, position the bolt over the end of the axle, then turn the bolt clockwise.
Grab a jar of anti-seize while you're at it, and before you put the new drums on, go nuts and coat the contact areas with the anti-seize.
Hope this helps,
Po
