Try to look at it from Oscar's view. He obviously has some issues that makes him the way he is, perhaps rehoming him would give him a fresh start, especially if the new owners want to help him (please don't think for a minute that I don't think you do, that certainly isnt the case).
To be honest, in your situation with your young boy, i would be considering exactly the same - it takes only seconds, and if you are all on edge the whole time, then Oscar is going to be as well.
You know the couple who are willing to take him, so you can keep in touch, and if it doesnt work out with them you can always try again.
I know that it isnt much consolation, but it will give the couple something to focus on now their son is going to University. They can join COL for support as well.
Don't disappear from COL, and one day the right dog will pop along for your family x