Work with Georgia, don't break up the family. Gus would grieve losing his sister, and you would regret it. If she needs to be desensitized to deer then she's a work in progress and it will take some time because deer are (to a dog) very exciting. As for all the other noises, she is trying to protect you.... I know that sounds like an obvious statement, but I think most will agree, the most important stimulus is "US" because they know their job is to protect us and our homes. Being outside is similar to being on the front lines of a conflict. She's your forward guard and it's up to her to keep evil away, so, maybe keeping her in where you are the leader and she knows to stand down because "The Boss" has got it and everyone is safe. Just an idea. I don't understand all of your dynamics, but, I'd hate to hear that you broke up the gang due to her doing her job, no matter how over the top that she does that job.
As for my dog...she never barked until she was six or seven months old. Silence was all I ever got and I was disturbed by it. One day at the dog park a Giant Schnausser stood in front of her and kept yelling at her and suddenly WOOF! It was a big dog Woof!, Big, Earth Shaking and Defiant! I was so happy, but when I reported it here at the Forum I got my ass kicked for approving that she had done it. All sorts of dire warnings and BS about wanting a dog to bark. Poop on them, none of their dire warnings came true. She only barks when there is a need, and she only uses that Earth Shattering Defiant bark when she is repelling an invader. And I thank God for that scary big dog bark...she keeps us safe. Nobody messes with the big dog when she delivers with one of those.