Aggression in a single dog home is definitely something that can be fixed, however it will take time, patience, and consistency. Also, it must involve the entire family, which means the kids (as hard as it sounds) will need to be involved, and try not to fear him. He is still young, and in his prime learning phases. You must start at basics again, and implement the nothing is free training. Make him work for things such as treats, food, pets, coming in or out, etc.
I know that quite a few members will chime in with their methods & things that have worked for them. You & your family need to regain the "alpha" position, and show him who's in charge. I know that it can work out, in extreme cases you can get a behaviorist to come in and help train with you and the family. Do not give up just yet, once he works out his issues, he'll be fine. Believe it or not, Tyson still has random outbursts of aggression. Very very random, and seldom, so its something that I have to work on constantly regardless in terms of making sure he realizes who's boss. I rescued him at the age of 2 1/2 almost 3, and he's now 9. It took work, and dedication, and lots of crating in the beginning, but he got the point. Now if he does for any reason, you can immediately tell he's sorry right after, he'll bow down in a shamed position. I wish you much luck, and keep us posted on his progress.
Here's a link to the thread - for nothing is free: