In any low game, the lowest 5 cards win that side of the pot. A2345 is the lowest possible in most cases. The A2456 you mention is a hand I would bet a lot of money on as it would win a majority of the time. Most have a low limit of an 8, which means the worst possible low that would qualify would be 87654. To determine the winning low hand, start at the highest card in each and work your way down. For example:
A2346 would beat A2356 and would lose to A2345