I would be inclined to bring a bed out to 12ft in an S shape all the way down the right hand side and turn that half into a woodland area. With some tall shrubs, Holly, bluebells, cowslips, some ferns and primulas. I would cover with a dark mulch and aim to have a hidden bark path winding down the middle of the bed flowing the S shape leading to a seat in front of a mirror on the bottom fence that could only be seen when on the path. I got a bit carried away but I did this to part of my own garden and I love it. Yet to get the mirror!

What a fantastic suggestion! Be careful with choice of ferns though - not all will like it so dry. Put a photo on here when its done. Also you might reseed the shaded part of the lawn with shade tolerant grass seed.

you also can have the trees taken out ofcourse . bye the look of it with them out the way you will have a clean slate to design within reasen ofcourse . when i look at the first picture its almost like a whole circle just about .it acured to me that you could have a path made out of different size circles kind of randomly placed and different sizes . even different hights with raised round raised beds and or sunken ones finishing at the end of your garden with the largest circle for seating etc . you could even have a raised water feacture along the path and i use that term losley lol . its easy to do tjhe circles . you just bang a peg in the ground tie some string half the width of your circle and pull it tight , spin it round . perfect circle . you can have the circles overlapping and have different textures for each circle ie one could be a planter . you could put decking on a few of the circles and slabs on the others or pebble dash or round cobbles . in between the circles there is enough room for some subtle planting . to get a natural looking wavey line going along the trees you just unravel a normal hose pipe and lay it out in the kind of shape you like then go in your bedroom and look at it from a distance . take your time over a cuppa rosey lee etc . i hope this may well help you to a lesser or greater degree . take care bye for now x x x x .

Besides being a massive project to remove the trees, it looks like only a few of them are actually hers, Np.
As for rehabbing the soil, I would put down a cm of good, black compost, 1 kg of blood meal for every 9 sq m, 3 kg of kelp meal per 9 sq m, and a good blend of micronutrients--we use True-green Citrus Grower's Blend here, and I'm hoping something similar is available in the UK. If the soil is very acid, some dolomite limestone would also be beneficial. The compost, blood meal, and limestone will probably need to be re-applied 1-2 times a growing season, since the trees will use up the nitrogen from the blood meal, the compost will gradually decay away, and the tree leaves produce acid to dissolve the limestone. Each year, the soil should get better.