Christy, please try to understand. Long ago, many rescues took dogs such as Sid. We all know that dogs placed in the right home often can be rehabilitated. You have obviously done a great job.
But as both a breeder and rescuer, I have to object to your disagreeing with the previous owner. When a dog gives a single bite, even one, if you place that dog, you open yourself as an owner or rescue, up to serious legal issues. I have known two rescues shut down due to the expenses related to placing dogs with bite history. So from that viewpoint, you have to ask if you have a right to risk your family's finances or the rescue from helping so many animals, just to save one. Further, you have to ask if you have the right to RISK someone being severely bitten because you don't want to stand up and do what is a terribly hard choice, which is to put a dog to sleep. Ultimately, I cannot imagine placing a dog that has bitten several times. Sure, if the dog was hurt and bit, yes. But Sid has bitten from being startled. He has what we call a very low bite threshold. All it takes is ONE idiot visiting the home to do something stupid and get bitten.
Would I personally have ANY qualms about taking Sid? No, of course not. It is obvious that he has done well with your family and can be managed. Sadly, I can't risk him upsetting the balance between my 2 bitches. I honestly thought about it, just so you know.
And I am praying that the placement works out, but please, cover yourself with a full release of responsibility from any liability if he bites. It may not hold up in court, but if you include his bite history, it should help. It will be a rare home that takes an older dog who has such a history, so hopefully her connection to his line will help. Please let us know. And if she is anywhere near me in GA and needs any help, she can call on me– though it sounds like she is experienced and will be fine!