Aly, I am so sorry you are in this situation.
I know how much you love Harley and want the best for him. I was in a similar situation, we were going to adopt a little Schnauzer from a girl who didn't want to keep her because she was pregnant and was afraid the dog would attack her child. They drove the little Schnauzer down from Los Angeles and we made the mistake of introducing them in our home and Perry (Schnauzer) without any warning attacked the little one. Well we kept trying to get them together and after him attacking her three or four times knew it was impossible. They did adopt her out to
their groomer who always loved her.
I was thinking maybe it would be better if Harley is very territorial to adopt him out to an older person who would give him all their attention, or a couple with no small children or a couple with no other dogs.
Good luck, I do believe you are doing the right thing for Harley and Shiloh.