Hazels (Cobs) are not self-fertile, so you do indeed need two plants of different named cultivars (varieties), or two seedling grown plants from different sources (rather than 2 plants of the same named cultivar).

Hazel trees do take a good number of years before they fruit reliably, so even though yours have grown vigorously they may only just be old enough to start bearing fruit, and the crop should improve each year. The nut crop can also be affected greatly by the weather at the time the tree is flowering since they are wind-pollinated and flower in the middle of winter.

If you do keep both trees you could also try a process called brutting whereby the ends of the shoots are bent downwards and effectively snapped and left to hang (still connected on the underside). This causes a physiological effect to the plant and makes it produce proto female flowers in more buds that are now forming in the axils of the leaves of this years growth.

Just searched for it and found this: http://www.ashridgetrees.co.uk/Cob-Hazel-Corylus-avellana-maxima