They will never flower if you store your bulbs indoors. The bulbs must go through stratification - winter. They must go through x hours of cold (below 40F) in order to bloom. This is why we plant spring bulbs in the Fall. However, containers are prone to freezing which introduces another problem. Can you move the containers to a sheltered location? The garage?

Dutch Irises, in general, flower in spring not summer. If you bought the bulbs late this may be why they didn't flower this year. Follow BGs advice and, whether they flower or not give them a weekly feed of half strength tomorite or similar once the leaves are up in spring until they die back naturally.

Dutch iris (I. x hollandica) is a hybrid of I. xiphium and I. tingitana. The parents are native to southern Iberia and northern Africa. (I would never have known about this if I hadn't looked up where Dutch Iris come from). This makes them part of the winter-growing group of bulbs which need a frost free winter and dry period in summer. I was curious about their origins because they do very well here while other irises fail, and it all comes down to stratification, which I can't give the other types of irises. While planting in the ground and mulching may keep them safe, a container will cause problems, as Bathgate said; but I wouldn't let them get below 40°F for very long, and I would not let the soil dry out completely. Mine get a dry summer and will start growing again very soon.

Mine do fine outside all the year including some frosts in winter and far too much rain in some years (like this one...)
In Caithness though it will be a lot colder.

Ours have been in the garden for over 25 years in Moray. This has included some very cold winters and very wet summers!

Mine grow right along side my daffodils & tulips - they bloom after the daffs, but I treat them all the same. I never dig them up. If they are planted at the right depth, they will never freeze but they need that winter chill. A layer of mulch on top is a good idea. Not sure about planting in pots.