Red Kites building a nest in our garden!

A couple of weeks ago, Red Kites were busy all day nest-building in a tall Scots Pine in our garden (boy, were we excited!). Then another pair arrived on the scene one day and I witnessed a huge display of dive-bombing, upside-down flying to lock talons and tumbling to the ground, and other amazing feats.  Since then there has not been so much activity - we see them maybe once or twice a day visiting the tree with sticks, or sitting sid-by-side on a branch ... but they  are being much more discreet.

Why??  I read that Red Kites often build several nests before choosing one.  Is our nest a cast-off now? Or were they just scared-off being too open and brash about their new home?

I do hope they stay around because we get an amazing view of them flying right past our bedroom window!