I am so sorry for your loss. Let me first say that these owners are irresponsible and are required to keep their dog in their own yard. However that doesn't mean that they will. Is there any way that you could secure the fence from your side. Or maybe even if they got another dog to not put it in the yard unsupervised since they know that the neighbors are irresponsible. I am not saying it is their fault just that they need to be responsible for their dog since the neighbors aren't. I also know that chihuahuas can bark a lot and it might make their dogs good targets for this powerful animal.
That being said dog on dog aggression is not the same thing as dog on people aggression. I own pit bulls which tend to be dog aggressive. I have a 6 foot wooden fence around my yard and my dogs are only let outside for short supervised times to do their business. I also walk my dogs on short strong leashes. I would not want a strange dog running up to me and mydogs uninvited. However any person child infant in the world could do anything they wanted to these dogs. My son frequently tries to ride them like horses, run toys into them, pull their ears etc. and they have never shown aggression to people. I have also read many books about animal behavior in an attempt to be the best advocate for my dogs that I can be. The areas of the brain that control animal aggression are different than those that control aggression in general.
I am not saying that this dog is not human aggressive just that it is not a given. Unfortunately the laws are such that in most states dogs are not considered aggressive unless they bite a person. I tend to agree. Dogs are not human as much as we love them and want them to be members of our family they go by a different set of rules than we do. Was anyone outside to witness the attack. The husky may have felt that she needed to dominate the chihuahua. I know that sounds crazy to humans because of course the chihuahua is 5 pounds and the husky 100. However we are thinking of this from a human perspective. Animals don't rationalize they go based on instinct. I am sorry if this is not easy for you to hear.
Once again I want to emphasize that the neighbors are irresponsible. Anyone with a dog whatever the breed is responsible to keep their dog restrained in a yard or on a leash however we know that this does not always happen. I also think that your family has the right to let your dog in your own yard. However if the fence is shared is it really secure? I would advise that you get a fence at least along the line where the huskies are that is not connected.
I do believe that the neighbors are responsible for your vet bills and the cost of the dog or a replacement. I know that nothing can ever replace the loss of your dog and I am so sorry that you have had to go through this. I would go talk to the neighbors and see what solutions they have for keeping their dogs contained. Maybe you could even bring along a copy of the leash law in your area.
I wish you all the best
A.