Do You scold him, if you discover poop in his crate? As a good boy he might have generalized that you don't like him to poop/don't like poop. That might be the reason behind his shy behavior outside: he might be trying to reach a 'safe' distance from you in every situation when poop is around and especially when he himself is about to produce this 'thing, that makes mommy so angry'.
Possible solution: just stop scolding at home, better look completely relaxed and happy when you come back and take him out of the room in a friendly way, before you start cleaning. Difficult, I know!
Talk to your vet what to fed and try different times/different food for their meals - to lessen their need to eliminate during the time while they have to be crated.
Surely you give them a good possibility to eliminate before you leave them? That, combined with the right kind of food and the right time to give it and no scolding at all connected with poop should help over some time.
How to walk a dog that has this kind of problem?
Arrange the food and feeding time according to the walkies-schedule.
Bring him out for long poo and pee - stops in a quiet environment
Praise and give treats for eliminating there, then start to walk to somewhere interesting for your dog
- turning back as soon as they have relieved themselves will act as a punishment for that - they would rather stay outside longer so by turning back as soon as they did it you teach them to hold it longer)... if the interesting walk starts, as soon as they did 'it', the learn to hurry up - which helps, if sometimes you are in a hurry.
All quite difficult with 3 dogs with the same kind of problem... probably best done seperately, first with the former 'good boy', even if that will take up some time every day, until it starts to get better. Better to spend time walking than cleaning dogs and crates...