Answer: It sounds as though you can distinguish between male and female blossoms, but for the benefit of anyone else reading this question who might not know the difference, male blossoms are attached to a straight stem and female blossoms have a small swelling just behind the bloom, where it attaches to the stem. Squash plants develop male blooms first and after a week or two begin to also develop female blossoms. That's why fruit never develops from the first blossoms on the plant.
Even though your plants will become overcrowded as they mature, they shouldn't be overcrowded now, so competition shouldn't be an issue. For future success though, transplant them so they each have a 16" container. If the female blossoms are not developing fruit, the likely cause is poor pollination. This can happen if the weather is too cold for insect activity, or too hot (pollen becomes sterile in temperatures over 90F degrees), or if conditions are too wet. Zucchini are such prolific plants that no fruit set this early in the season should not affect the harvest later in the summer.
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