They are crab apples by the look of 'em.
We make crab apple mint jelly from ours:
3lbs crab apples
1 & 1/8th pint water
1 & 1/8th pint vinegar (we always use white vinegar)
Sugar
4 table spoons finely chopped mint
Wash the crabs, cut in half & remove any storks, blossom ends & bad blemishes (& grubs!   

  )
Place in large pan with the water, don't be tempted to add more water.
Simmer 'till the crabs are soft & pulpy, then add the vinegar and boil for five minutes.
Strain overnight through a jelly bag.
Next day, for each pint of juice add 1lb of sugar, then bring to the boil, stirring 'till all the sugar is disolved.
Boil rapidly 'till the setting point is reached (about 5-10mins, in our experience).
Add the mint & stir.
Pour into hot jars cover & seal 
MW