Wrestle the staples out with needle nose pliers. If that doesn't work, cutting them flush using snips would be plan B. Really you just need to get them out of the way so you can put the front of the drawer back where it needs to be.

Yes, I would think to put the brackets on the inside front and secure them with fairly short screws. One bracket on each side would probably be enough, but I don't see the harm in using two on each side.