You can remove the two small bolts, but it won't help an awful lot. Unless you remove the single large bolt, you won't be able to maneuver the bracket so it clears that part of the body.
The bolt with the broken head isn't a problem, if the head is completely gone. The rounded-off nut is more of a problem. See if you can get some vise-grips or some such on them, and turn the bolt instead of the nut. Try heat, penetrating oil, vibration (like hitting with a hammer), and all of the usual "stubborn-bolt" methods.
A drill or cut-off wheel would be a last resort. You can even cut the bracket itself and botl in a new one.