It looks like Wooly aphid. This is a bit of a swine to get rid of because the aphids are protected by the grey, almost fungus-like grey stuff you can see. And, yes, it does eventually cause the bark to split and peel. It is commonest in drier, warmer parts of the country but can strike anywhere. The usual way of dealing with it is to scrub the bark with meths but it gets messy, so wear gloves and an old coat.

Some rootstocks are very prone to woolly aphid. The MM series have moderate resistance to woolly aphid (MM106 is the most common) but I don't suppose you know what rootstock these are on, especially if they are old.

Dwarf trees succumb very easily but I take it these are full size which means you could have had it for years without noticing. I suggest cutting infected branches off where possible and using the meths treatment where you can't.

It is a bit difficult to tell from your photos so it just could be Botrytis. Though this is less likely. If the meths doesn't work then get some Bordeaux mixture from a good garden center and spray once next month then again in March, that wouldn't hurt it anyway to be safe unless of course you are pure organic, in which case you will just have to cut down and burn the trees and start again. But I reckon it's the woolies.