Welcome to pets.ca Antonroder
Your situation sounds serious enough (especially when young children are involved) to consult with a behaviorist experienced with this type of aggression. Without actually seeing your dog and the dynamics of your family, it's very difficult to give advice over the internet.
You'll find a list of trainers here: The Canadian Association of Professional Pet Dog Trainers http://www.cappdt.ca/trainers.jsp
. Put in Manitoba in the province field. I suggest you research well and ask for (and please verify), references.
It must be difficult for your family. I hope you can all learn to work with him