I have to agree with Sheilah about that point. I do not feel that euthanasia is the worst thing either. But it could be because we had a similar situation and ultimately had to consider the welfare of all the animals involved in it.
A friend of ours, which we had told her it was not a good idea, decided to adopt a deaf and partly blind border collie/aussie cross. Double merle, high white. Sweet boy with a nice personality. If you were always with him or he had another dog around to keep him assured that everything was okay. And this meant he had to be able to physically be next to the dog in the same space, be it outside or in a crate.
My golden grew up with him as his best friend. My roommate's aussie not only put up with him following him and nipping, running into him while we were out and about, but kept an eye on him so that we didn't lose him. We tried time and time again to find him a home, because it was very hard to arrange our lives if we couldn't take him somewhere, and a dog always had to be left with him, so someone was left out if we couldn't take Murdock somewhere.
He kept coming back when we would try to rehome him. If left alone, he would bark and carry on all day. He would break out of crates to the point of hurting himself. He wasn't always good with other dogs, not because he was malicious but because he couldn't hear them saying that it hurt. It was a cause for a lot of headaches and a few vet trips from him inadvertently hurting another dog.
After the last time we found a home that worked for him for a month, things just got truly bad. He was getting so pushy with the other dogs he had to wear a basket muzzle to keep him from hurting the aussie. Which lead him to hit the dog with such force you could literally hear the air come rushing out of his lungs. He kept biting the 15 year old shortador's hind legs, which was something that caused a lot of fear for the old man if he had to go outside. And my golden, who would love to play with him, was actually trying to avoid him.
When it was decided that my roommate would be keeping a dog that was a co-own with a friend, a young puppy who was still developing, and really no other hope in sight for a home for him, we finally made the choice to have him euthanized.
It was not easy. It was a very long time coming. And I know it haunts my roommate still that we had to do it, but for Murdock it was the best thing. He had such bad anxiety about being alone, he couldn't really communicate well, people always thought of how wonderful it would be to have a special needs dog, but no one ever stepped up once our friend couldn't keep him around. We knew we would end up with him. Neither of us were happy about the situation as a whole.
Fear aggression is not an easy road. It's a long one and a very involved one with a lot of triumphs and pitfalls. While I definitely can understand not wanting to euthanize an otherwise young and healthy dog, if you cannot find him a safe place or find a way to keep things safe with your child on the way and all the other dogs in the house, it is a far less cruel thing to have him with people who care at his side, then alone and likely more scared in a situation that could lead to all sorts of bad things.