Not only part of the landscape [member=81282]juliem[/member] but still a habitat for wildlife. Dead trees and rotting wood give homes to all sorts of beetles and other insects, nesting holes for solitary and bumble bees, nesting sites for birds and bats which need holes, perches for birds, especially birds of prey, but also blackbirds and robins which love to shout out their glorious songs from the top. Even when a dead tree falls it carries on providing for other things to grow. The wood rots down returning the carbon to the Earth, it provides shelter for new trees to grow, flowers and fungi to thrive. Creatures which live in or on dead wood are struggling these days because of our tendency to clear up 'mess' which includes dead trees.
Your split tree may well not be good enough for big timber, depending on why it split, but yes, at only 50 years these trees are still babies compared to what they will become. I appreciate your dilemma when some trees are growing into or over your house. Snuggled up to the foundations is a favourite site for tree seeds to germinate. We have a couple here too, luckily only an ash and an elder, but any tree seeds which germinate in my rockery get the heave-o straight away, or at least are carefully dug out and planted somewhere they are wanted.
Well done to your son for planting oaks in the hedgerows. They are a nuisance at hedging time - we mark a white spot in paint on the fence post nearest to each standard tree so we can leave that as the hedge cutter reaches it. It's a real nuisance but the care you take now will pay off in years to come, even when the hedge has gone the oaks will still be standing to mark the hedge line.