How do I get the broken piece of the caliper bolts out of the part where I reattach the caliper to the rotor

To remove a bolt sheared off flush, you need a center-punch (a drift pin with a very sharp point) to punch the exact center of bolt, an EZ-Out tool, you can buy a single one wit the proper size drill bit, don't have to buy a set) Punch bolt, in exact center. If you have a drill bit index it's easier to begin with a small bit, then go to bigger bit. But not mandatory Hammer in EZ-out, and I mean WHACK it a good one, turn tool counterclockwise and it should grip and un-thread bolt. Buy proper bolts for new ones.

Take a dremal And cut a stright line down the center of broke off bolt deep enough To isert a impact screwdriver use impact screwdriver to remove bolt becareful not to cut to Wide And dont forget to use lots of wd 40on broke off bolt