A v-belt wouldn't stretch that much. After loosening the alternator (and power steering pump) and sliding them in to their inside adjustment and the belts still won't go on, my guess would be that someone either changed your pullies at some point or you have to wrong belts. In either case just take them back to the store and ask for a couple that are maybe an inch longer. Take your old ones with you, they should be able to measure them, or just match them up to a new set.