"Oxymel of Squill"
Your trees are suffering from Blossom end wilt - a form of canker
No need to panic
Get out your secateurs now and cut back to healthy wood. Dispose of
the wood (burn) and clean secateurs with methylated spirits so that
you do not spread it to other apple trees when you prune them
One of my trees tends to suffer more than the other - you can apply a
preventative spray now and repeat every 14 days using Diathane 945
which is a fungicide that will help.
It is unusual though that this causes loss of crop. Cannot offer a
reason as to why though
Regards
Clifford
Bawtry, Doncaster, South Yorkshire