Sistering means attaching a flat piece to another piece.
In woodworking, if you had a floor joist that was rotten or had too many holes in it you would put another joist right next to it and attach the two together.
If you had the correct shape you could cut it out of a flat piece of 18 gauge plate steel and have it welded to the existing bow forcing the existing bow back into shape.
One of you photos looks like the bow is cracked where it is bent. Doesn't look like it could be streightned easily.
Most likely the top will have to be removed from the bow to make a repair.
And yes there is some material in the bow that the top can be stapled to, mine (67 dart) has a hard board like material
