Can i get permission to build small two bedroom bungalow in garden for parents we are not overlooked at all?

i have a very large garden to which i would like my parents to build a bungalow in we are not overlooked at all and we are by a river and our house is and old water mill in conservation area so it would be built in stones as the old building so it wouldnt look out of place basically we will build another small barn really in keeping with the area.