Yellow Black Mouth Cur

Question
We rescued a male pup(Dan)from a shopping cart in a parking lot about 4 years ago.Vet claimed he is a YBMC.He had been terribly abused.He still carries the scars.He has one that runs across his head and down the side of his face.It looks as if someone hit him with a board.He has always been very nervous around new people and other animals.It took him about two years to even trust us enough to start playing with us.He has been a great family member.I never had to house train him and he has never even so much as gotten into the trash.Almost 3 years ago we adopted a female pup(Jazz)from a shelter.She is the size of a terrier.1 year ago we adopted another female pup(6 months old at the time...Whiskey)She is about the size of a Chow.Then a few months later my daughter brought home a male pup about 8 weeks old.Dan kept attacking this pup.As the pup grew it got worse.It was never a dominate thing.Dan would try killing the pup by picking it up and shaking him.My daughter and her dog moved out and I thought I would finally have some peace.But now Dan is attacking Whiskey.The females are spayed Dan isnt because of him being so nervous about everything I would be worried about the whole experience traumatizing him more.I can't stress enough how frightened he is of everything.He is a little better now but not by much.My friends would bring their dogs over and he would hide in a corner and shake the whole time.All the sites about this breed says not to punish them by "spanking" them a stern voice is enough.To this day you can't even raise your voice around him without him hiding and shaking all over.He has just started attacking Whiskey for no apparent reason.Again he is trying to hurt her not just show dominance.The first couple of times we weren't sure if she had done something or not.The last time Whiskey was laying down and I watched Dan walk by her,stop,look at her then jumped on her.It happened very quickly and that is when I knew for sure we had a problem.I made excuses for him with the other male dog but I can't find a single one for him this time.According to the sites about this breed they are fine with other dogs if they have always been around other dogs and he has.We have kept them separated since the last time because I don't want them to hurt each other and also I have a 4 year old daughter that I don't want to take a chance of her getting caught in the middle.I don't like separating them because I don't feel it is fair to either of them to keep one locked up while the other is with the family.As for Jazz he hasn't tried hurting her yet but if he does she is so little that I am afraid he will kill her.With this behavior seeming to come out of nowhere I am also worried that he might turn on one of us.I have considered finding him a new home but I don't know how he would react to new people and new surroundings.So I am considering on having him put down.Before I do though,I want to see if there is anything else I can try first.Putting him down is the last thing I want to do but I need to consider the safety of my family and the best thing for him.Please if you have any suggestions or thoughts on what else I can do let me know.Please.

Answer
The problem is that he does not feel safe and secure in his place in the pack. Nor is he confident in his pack leader. Which is you.
Go to alpha dog boot camp on the web to learn how to establish and maintain pack order in your home. Your dog will definitely relax. Rehoming him is not an option. Retraining, and restructuring are your only options other than euthanasia.
Also purchase or get from the library Cesar Milan's book Be The Pack Leader. Get him walking. EVERY day, forty five minutes minimum at heel. This is not a pleasure walk but is part of restructuring his mind into a calm submissive state. IT WORKS believe me. Tire him out, get him out and moving until he is tongue hanging tired at least three times per week PLUS the walks, not instead of. IF you can get him into an obedience class. DO the steps the website tells you to do. It will change his life, and yours
Good luck
Cindi