Hello - Denia is a little different to the Costa Blanca South in that the surrounding area consists of fairly low density urbanisations which house mainly Brits, Germans, Dutch and Belgians. So yes there are Brits around although the place is not overrun with them. If you wanted more contact with British people areas like Javea and Jalon have a higher density of British people along with British stores and a higher number of british restaurants. All the areas are also served by British communities e.g. http://u3valldepop.com/.
School wise you didn't give ages or whether you want them to go to a Spanish school but the local English school is http://en.laudeladyelizabeth.com/
If you need any more help shout .