Since your fifth person is under three years old, you can stay anywhere. All resorts can accommodate four plus an infant under three. The value rooms might be a little small since you will be using a crib (not a lot of floor space), but it is certainly legal and just depends on how much you will be in the room and how much you want to spend. Some of the deluxe resorts have a daybed in case you wanted your mom to have her own bed, or you can request a trundle at POR if she wants her own bed.