1st thing is to find out if it is still loaded. Many were stored loaded, ready for use, then not used again - thus still loaded. Use the rod inside then compare outside the tubes. Be aware it has breech plugs with hollowed noses, so the rod should reach back to within about 1/2" of the nipples. Appears to be a hooked breech gun.

The muzzles are nasty and the bores probably are as well by the looks of the muzzles - hard to say.

Once you know it isn't loaded, lift the hammers off whatever is left of the nipples and if there is a hole in the ends of the nipples, plug with tooth pics.

Then carefully fill the bores with varsol or some thin solvent and let sit, breech down, off the stock. Look for leaks. If damascus and probably are, rod can run that is virtualy invisible. the solvent will find it's way out if it can. Any leaks of course, means it's a wall hanger.
That's a start. Judging by the looks of it, refurbishing will cost a LOT. Cleanup is something you can do, John for a display piece.