you probably just need to be patient. Did you buy all female plants or the mixed male & female plant? behind the female flowers there will be a small immature cucumber. if the flowers are dropping off with out development and you have male flowers take a paint brush / cotton bud and collect the pollen and transfer it to the female flower parts inside the flower.

I only have had 3 cucumbers so far but I am struggling to eat them. Thankfully the pet rabbits like an odd chunk or too.

Greenhouse Cucumbers
Keep the greenhouse warm and humid by regularly spraying or damping down of pathways. You will probably need to apply some greenhouse shading to protect the plants from scorching.

Always remove the male flowers from greenhouse cucumbers. Female cucumber flowers can be identified by a swollen bulge between the bottom of the flower and the flower stem that looks like a tiny cucumber. Male flowers just have a plain stalk so you can easily tell them apart.

I grew Marketmore outdoor cucs this year - 2 in the greenhouse and 1 outside. Had lots of male and females on the plant and took off the first cuc 10 days ago. Had 4 more since.
Are you giving them sufficient water ? Rightly or wrongly I fill up the base container up to 3 times a day,and feed them with comfrey liquid.
Give them more time and I'm sure they'll produce.

I bought 4 cucumber plants from Homebase and put them in a semi covered cold frame. I only water them and they are thriving with many cucumbers to eat.
In my opinion if they like the place they will do well.