Are all three amaryllis bulbs the same cultivar? Our best guess is that, much like people, each bulb is an individual and may require a different maturation period. Give them time and each one should come into flower eventually.
In addition, here are the instructions from our Gardner for Public Education, Sonia Uyterhoeven: Amaryllis do not require a chilling period. Plant them with at least one third of the bulb above the surface and leave one inch between the bulb and the edge of the container. Water your amaryllis in well when planted, but then keep the soil on the drier side until you see the flower stalk emerging. Once the flower stalk appears, start watering on a more regular basis. Amaryllis need a well-lit, warm place to grow until the buds begin to open. Then it can be moved to a cooler shadier location where the blooms will last longer. After the bulb finishes blooming, cut the flower stock close to the base. Grow the plant in a sunny location and add houseplant fertilizer regularly. Stop watering and feeding in August, and allow the plant to dry out completely. It generally will need an eight week resting period. In late September, cut back foliage and re-pot the bulb in fresh potting soil. Place in a sunny location and water sparingly until growth begins again.
Best of luck and happy holidays! ~ AR