Tough brake bud! Is enough of the bolt sticking out on eather side to grasp with vise grips? If their is you may be able to get them out by aplying heat with a propane torch and then soaking it with penatrating oil. If the vise grips do not work you could try the classic EasyOut. Remember before trying the easy out to heat the bolt and use penitrating oil on If this does not work you could always drill it out with a drill smaller than the bolt size. I have had good luck using the correct tap drill for the bolt size and then chasing out the hole with a good tap. I imagine your bolts are stuck in captured or welded on nuts. If all atempts fail grind off the old nut and welp a fresh one in its place. it.
Good Luck
Good Luck