Lizzie, myself and Jack & Sunny are all praying for you and your cats.
I don't think you need to be so hard on yourself, you are doing a wonderful thing by adopting the five fiv cats in the first place, you are opening your heart to give them a home. I'm sure that Ginger and Nougat will be fine and even if they have caught the virus then I'm sure you will nurse them well and they will recover and be fine. If the other cats are living a good life there is not reason why Ginger and Nougat can too.
I really hope everything turns out fine, you are a saint for being so kind to the cats, not many people would adopt a cat with FIV, and even if you may have to return them to the shelter, it will be of no fault of your own. It may be the situation wasn't meant to be but you gave it a try and that's the most important thing that you were willing to help these cats.