My son is 7 years old and was attacked by a rotweiler.?

My son was going into his grandmothers backyard to get a ball and was attacked by the neighbors Rotweiler. The problem is that the house is a duplex, the backyard is not split and they are also family members. The dog is vicious and has attacked on several occasions, but they want to keep the dog. My son has 15 stitches in his left arm and is now petrified of big dogs or even going to his grandmothers. I want the dog gone I dont care where or how but removed from the property. I am getting a lawyer and I will do what it takes. My only problem is am I wrong considering this is my husbands family. I have a lot going through my mind right now but my son comes first. I am just looking for some advice on how to handle this situation.