Debbie I really feel for you too as we have been there with Alfie and Mollie (the self-same Alfie mentioned above by Nicola). Not Alfie's fault and poor Nicola's loss was our gain. However, our resolution was not a good outcome and we no longer have Mollie. I think I would wait a little while to see if Morgan settles down after his op as his body won't know what's going on right now, while taking the advice of a behaviourist and your breeder, and a vet trip to make sure nothing physical is bothering him.
We had a really good behaviourist work with Mollie. We had exercises to reduce her frustration levels etc., but nothing seemed to work. She ended up pinning Alfie down sometimes a dozen or more times a day as he refused to fight back, and indeed became too wary to even be around her and by extension, us. We tried keeping her on a house lead at home (like you we had no problems outside) as suggested by the behaviourist so we could lead her gently away from a fight. Unfortunately, while this worked, she seemed to stack all her frustrations up and would trounce Alfie even harder when the house line came off, and blood was drawn. So for us, it didn't work, but a house line may work for you.
We decided both dogs must have been very unhappy in this situation, Alfie because he was on the receiving end and Mollie because she obviously couldn't cope with life with us for whatever reason, plus she did start redirecting onto us after a fight and for a few other reasons too. We have no young children here, but if we had I doubt they could have been together with the two dogs. As hard as it is to think of rehoming a beloved dog, you really have to think of the dog's quality of life. I really hope it doesn't come to that for you though - it may well be something you can work out with a behaviourist.
We've had another dog, Genie, living with us for 6 months now and, to date, she and Alfie have had no problems. I was starting to worry it was poor Alfie that was just a dog other dogs love to hate, but he's not.
Lots of luck and hugs.