As long as they haven't been used for a froe
or otherwise abused , it doesn't take much. Use a file to redefine the cutting angle and then a stone to sharpen. If it's badly pitted on the flat side , you will have to get it back down to good steel. Course sandpaper on a block works pretty good. If you are good with a belt sander you can do it that way, but it removes a lot of material fast! Clamp the belt sander upside down on the bench and hold the knife to the belt with the belt running away from the cutting edge. Use a fine belt and remember to take the dust bag off! Wear a mask of course and clean up well after. That fine stuff is nasty business. Try it with the block first, it may not need much and it's better not to risk it. The ultimate goal is a polished and flat surface on the flat side , so get it down to 600 grit at least (I polish with a felt buffing wheel and green honing compound to a mirror finish on my cutting tools) On the bevel side ,just the cutting edge needs to be polished.
This is of course if you are using it as a draw knife . If you are chasing rings on Osage , you don't want it that sharp or it will be too easy to cut into the next ring. As for the rust on the rest of it, sand it with 400 grit paper until it turns more black than rusty and rub a coat of oil on it. Wipe it dry and follow up with a coat of paste wax or two. That will keep it from rusting further and gives it a nice patina look of a tool that was meant to be used! A little oil and wax on the handles will also rejuvenate them. Make sure the handles are in good shape. secure or replace if necessary . The last thing you want is a handle to split /crack and drive a splinter through your hand as you are bearing down hard on a tough knot!.