Hazelnut Pruning

I have moved to a property with two Hazelnut Bushes, planted approx 30 metres apart. They appear pretty old and have multiple stems (approx 20 each) and are about 10ft high.

In the past 3 years I have only harvested half a dozen nuts from each bush each year.

I am wondering if I should give them both a serious pruning, back to one trunk even and hope this results in better nut production in a year or two.

We live in a temperate zone which can have frosts to around -5 degrees celcius in winter and up to +30 in the summer. We are in the middle of our winter now.

Hoping someone can help me?