Seems that your wheel cylinders have seized for good... There is another method, not so gentle as hammering. You will need a strong three-legged puller.
Rear wheels are a little easier. Remove the wheel, the grease cap on the centre of the drum, the split pin, and the 24mm nut. Back off the brake shoe adjusters (10mm square heads, and I will not be surprised if they are seized, too). Now try to extract the drum with the puller, by placing its claws over the ridge on the drum periphery. More than likely you will damage the brake shoes, but it is pointless trying to rescue them anyway. Better still if you disconnect the wheel cylinder hydraulic union and remove the wheel cylinder locating bolts (10mm) so that the wheel cylinder is free to come out.
The front drums can be extracted in the same manner, but you will discover that the wheel cylinder bolts cannot be loosened (you must loosen the backplate first-another story...). Make sure that, before you start pulling the drum, you have removed the locating setscrews (3 cross-headed ones on each drum). These can also be hard to come loose, and you may need an impact screwdriver, too.