Way to go Debbie! So your picture is worth a thousand words and eliminates a lot of speculation - the smaller plants are a bit too close together, I think. If you planted them on a "hill" of really rich compost, (like a couple of wheelbarrows full) you might get away with putting them that close together. The big, dark green, lush one has a nice space all on its own, and (who knows
) maybe deeper or more fertile soil there as well.
The second-best one, far right is a little bit crowded by whatever that is behind it but is doing ok. The other three, well as I said before, I'd remove all the flowers and give them a shot of fertilizer or at least a couple of watering cans of alfalfa pellet porridge, to see if you can give them a boost towards growing a few more leaves before they start producing. No doubt about it, you've gotta feed those babies for them to do anything.
Even if only two plants survive, I think you'll have plenty of squash, though. They're not quite as prolific as zucchini but pretty close.