We would want to spend the autumn in Istria along with my family, ca 3 months altogether. Any ideas where I can find a rental villa for a period like this? I tried Airbnb, but they seem mostly to work for periods of up to one week...
Finding 1 property for 3 months for this summer will not be easy, most short term rental properties do have some booked days already. Try www.fridayflats.com, they have about 4.000 rentals in Croatia, quite a good chance you will find something suitable for you and your family ;)