Bless you for taking that poor little guy, and it sounds like you're doing an amazing job. There are several people on the forum who have dealt with challenging rescues very successfully (I see Laurie responded while I wrote this book) , so hopefully they will give you some tips. Also, please contact http://www.havaneserescue.com/
if you haven't already, as they will have some advice on how to help Milo.
I have a dog that I now know came from a puppy mill. I found out later that well over a hundred dogs were found there despite the web site showing she had just one litter of Havanese. He came to me by plane and arrived a very frightened little puppy. He certainly doesn't sound like he's been through as much as Milo or Lucky but he has some of the same problems on a milder level. He has some fear aggression. He tries to bite and growl any dog that comes near us. He has bitten several people including myself, my son and his friend, he has had severe separation anxiety (has improved a little), he hated almost every food for the first year and a half, he still has potty accidents and leaks whenever he's scared or excited. He's always been just anxious and fearful. After being on this forum, I have realized how different he is from all the Hav's that were bred the right way in a loving home. He has definitely improved, but he still has biting issues, separation issues, etc. If you haven't already, I would consider hiring a good behavioral trainer in your area. The suggestions on treats were excellent (boiled chicken and chicken jerky are Marble's favorites). If you can find treats he loves, you can really encourage the good behaviors and make him want to behave. I'm sure you've worked with him by having visitors give him treats, but I think this will take so much longer because he is fearful and had several years of neglect under his belt before you got him. I think the key is that his progress will take a long time, and you need a lot of patience and consistency (which I see that you have). In terms of food, I had to try about 10 brands over the course of a year and a half to find one he'd eat. I finally resorted to a boiled chicken breast/vegetable diet that he loved, but you have to make sure they get the right balance. If Milo was neglected, then he was probably never taught to not bite, so it doesn't surprise me that he bit you. Just yelp and correct him, and make sure you watch him around people.
Christie, I had no idea that you were still dealing with so many issues. These dogs are so lucky to have such patient, dedicated people. I am sure that Lucky loves you, even if you can't see it sometimes. As I said, Marble still has accidents. He's almost three, and I've had him for 2 years and 9 months. Sometimes you may be able to improve it but not completely eliminate it. I do keep him in an expen when I leave.
You are both great to take these guys in and work with them so hard. Things will improve over time. Keep us updated.