Greek Easter falls on April 23 in 2006. Great time to be there if you have a local host, not so great for tourists.

Jenbel and Aviatrix' advice is excellent. Avoid staying in Heraklion proper, as it is a dusty, noisy city.

If the spouses/SO don't fancy driving, the town of Hania is pleasant enough to keep them happy for 1-2 days, after which the entire group could head east to tour the major sights. Hania is probably too far west to make day trips to the major sights relaxing, though.