Hi Mrs P
I've been to Northern Cyprus before though not with JY. I took Turkish Lira and used Euros in the airport only - that is if you fly into Larnaca. I didn't venture to the Greek part where Euros will be required. Apparently, you get a better exchange rate for your £ sterling to Turkish Lira in the banks in Northern Cyprus, though I got my currency in the UK.
Hope this helps.
Sylvia