I am afraid I am in complete agreement with JBL. I thought I had misread your comment about "can't take the cat back"..but, apparently not. I have never heard of a rescue operation that doesn't require you to sign something saying "I will return the cat to your organization if something doesn't work out". So, I would question that, first.

Next, I am a even multi cat household. My mom is an odd male household. Neither of us have had spraying/territory/gender related issues. I really think it has all to do with the alpha status established before the newbie comes along. My males are move snuggable...but, all my cats let me squish all over them...except for Minnie, but that isn't her fault.