Can you take him as a foster? I don't know if you have a little extra bathroom or somewhere that he can stay. It might be kind of dangerous to adopt him and put him directly outside. He won't know he lives there yet and may just walk away for good I know your husband and your other cats might not like the fact that you'd be fostering, but at least it would save his life and you wouldn't have to worry about him living outside. You might want to try some Feliway if you did bring him into the house (it is expensive, but might stop your kitties from spraying).

Good luck. I totally sympathize with your situation. I always want to save them all too, but I'm just not capable of taking every single one in