Very easy if you own the land behind the trees, just pull them with a decent rope and a tractor whilst someone chain saws the trunk, then tidy up. If there's a fence it will need temporarily removing. I would imagine £400 or so. A good 2 full days work for a decent chap. The oaks, (which look more like birches to me) would need climbing and bringing down with some consideration for the buildings, but whilst not in leaf they look straightforward. Getting `em down is fairly easy, tidying up is the PITA.