I'm fostering a little boy that had some behavioral problems and he was scared to death the first week and had panic attacks. I think the thing that helped him the most was taking walks together as a family. Cesar says that a dog needs a job and walking and surveying the neighborhood is a great job for a dog. When you walk all together it establishes a bond and this will help him realize that you and your husband and your female and he are one solid pack. It's going to be a little harder for him to trust, it sounds like there was some abuse in his past, so it will take patience on your part, but it can be so rewarding when they finally feel safe. Another thing I suggest is to make the dog sit and stay before you place the food on the floor, this helps teach them that you are the pack leader. Best of luck, but if you walk daily, I think you’ll see some changes in a couple of weeks. It will probably take months before he really feels safe.
The training technique of Nothing in Life is Free, helps many dogs, you can google the words and find more information, but it helps build the dog's confidence. Remember, and aggressive dog is a scared dog.
Nothing in Life is Free
By the way, to the other who have commented on the trial basis, this isn't that unusual when doing it among private parties. However, I hope you are the type of person who doesn't give up easily, there are answers out there that will help you.