Try thinning the fruit when they first setas in the peach trees
response above this will get the Apple tree to concentrate on
producing those ones left with more nutrients you should try to pick
off and leave around 2-3 per truss.

Do you also regulary prune the tree in the Fall/Autumn months?? this
could be having an effect.

If this still gives you problems try as sugested the soil test.
although i think this is a prunning issue or to many fruits for the
tree to support

www.gardeningcareblog.com

Hope this helps