James,
Do not be put off by pruning, it sounds a lot more complicated than it
really is. Just remeber the advice in the previous post -
If you follow the regular advise for winter pruning, removed dead
diseased, dying, crossing branches and reducing last years leader
growth by 1/3rd you won't go far wrong

What part of the o****ry are you in? Are your trees still dormant. If
so you still have time to prune them.
As your apples haven't been pruned for 15 years they need some
attention. Do you recall what varieties you have got? If you know, I
can tell you which are Tip or Spur bearers.
You would be unlucky to have selected all tip bearers. Most apples are
typically spur bearers.
I know you said that you are looking for fruit, do the trees flower and
produce any fruit?

As far as the quince goes, the lean sounds dramatic. From your
comments it too must be an age. Has the wind blown it over or is it
growing just with a lean? A friend has a Crawley Beauty that has must
have been blown over when young; a good six feet of the trunk lies on
the ground before it goes vertical. Hasn't done it any harm.

If you have any queries, feel free to ask, on or off list

Clifford
Bawtry, Doncaster, South Yorkshire