They have flowers and look healthy, and have been planted since May. If they are both male plants, will they grow zucchini? Flowers are falling off, but I don't see anything growing.
How Do You Know if They Are Male or Female
Certified GKH Gardening Expert
This is typical behavior for a squash plant. They will produce mostly male (non-fruiting) blossoms early in the season and will gradually start to produce more female blossoms as the season progresses. Give it some time and you will see it start fruiting. Female flowers will have small fruit behind the flower. This article will help determine male from female: https://www.gardeningknowhow.com/edible/vegetables/squash/female-male-squash-blossoms.htm
If you are seeing fruit or female flowers but they are falling off, this article will help: https://www.gardeningknowhow.com/edible/vegetables/zucchini/zucchini-fruit-fall-off-the-plant-before-they-are-full-grown.htm