One of those small air disc cutters with a 2 or 3" blade should be able to cut the bolt at bottom side. Just don't cut metal or not much anyway. OR, I use a 4-1/2" grinder many times.
Did you try to pull up on step to lock heads in better? If they are tight, better to just tighten more till they break off. They are pretty small bolts, break easy.
