Sometimes the chainring bolts sieze with corrosion that form in their threads if the bike ir ridden often in wet conditiond. Spray the bolts with a release penetrant like PB Blaster. Let them sit overnight so the stuff wroks its way into the threads and corrosion then try unscrewring them again using the slots at the back of the barrel nuts for more leverage. If they still won't release from each other after a couple of repeat applications of the penetrant, you might have to graduate to the careful application of a bit of heat from mybe a butane torch but be careful, as the aluminum chainrings and crank spider cannot take as much heat as steel can.

Chombi