I grow apples and grapes and have made some apple-grape blended
beverages that are outrageously tasty (some also with honey too). I
encourage you to obtain scions of well known cider apple varieties that
can be grown in your climate, as those four you are growing, while being
famous and tasty eating apples, won't provide the full range of flavors
you can get in cider. I don't know what the import controls are for
viable plant material in your country, but surely there must be some
ways you can get other varieties? In the USA some good types I am trying
include Anna, Harrison, Reverend Morgan, Cox Orange Pippin, Newtown
pippin, Mutsu (Mutsu aka Crispin is sterile, so needs a good pollinator
nearby), and Granny Smith.
You can also
plant seeds of apples and if they produce good fruit you can name it
yourself. This is obviously a long term project!
Grape varieties I have successfully blended with apples are Cabernet Sauvignon, Grenache, Thompson's, Barbera, Syrah.
I
don't know if these will do well in your climate, though. I imagine you
need apples and grapes that will tolerate a colder climate. I suggest
you look into similar growing zones and see what will work with your
growing season and chill hours. I would suggest Anna first, as it is a
good all-around apple for eating, pies, and cider, it blooms early,
produces early and is a heavy cropper. Also if your customers like Gala, they will love Anna! My Reverend Morgan seems to be a heavy cropper too, but requires a longer season and produces a much tarter apple better for cider and cooking. Harrison has a long history in the USA for cider too. Northern Spy and Macintosh are two other popular varieties known in northern states that are great for your cider and also will sell well for eating.
I am sure the UK folks will have a completely different list of good choices!