Sick apple trees – anything I can do this autumn?

We have about 6 (out of about 12) apple trees that produced few leaves this year, leaves have brown spots, are dry and fruit is sparse. They look sick. The trees are about 13 years old, dwarf, not sure the specific types, but various types. We have lived here 3 years and the past 2 years have been healthy and produced lots of fruit. This year, lots of blossoms, but few leaves and then little fruit: and fruit that is produced had hard brown skin, cracked/woody. Even the trees in the orchard not effected by the brown spots have produced little or no good fruit. I guess it must be some form of apple scab disease (from reading your database). Is there anything I can do now (sept) for them? I really want to look after them. Is this a result of over-pruning? My poor trees! Please help. Thanks.