Pit Bull/Boxer Mix

Question
Hello.
I have a two year old Pit Bull/Boxer mix.

He is friendly and he loves to cuddle.

He was given to me by my cousin who never treated him well and had a daughter who used to poke him in the eye unintentionally.

He snapped at her, and they were going to put him down, so I opted to take him before the could seeing as how I am college student with no family.

He has come a long way since he and I have become friends.

Now to my question.

Duce is very aggressive towards some animals, but only for show. He will bark at the dogs in the other apartments when he hears them, and then whimper his way up to my lap.
On other occasions, as with my mothers dogs who weigh 150 pounds a piece, he was on the complete offensive trying to bite them through the fence.

The final thing.
For Halloween I dressed him up and brought him to visit my friends daughter for her Birthday.
He was great around everyone but when she came near, he was unusually still.
He didn't growl, but he wouldn't wag either.
No one noticed the behavior, but I caught on and didn't want to risk anything so we left.

Would getting him fixed have any effects on those issues?
What are some things I can do to help him?

I love Him, and I know that Pit Bull breeds are very misunderstood and I don't want him to become just another statistic.
Michael Vick Helped enough.

Thanks for your help.

Answer
What you can actually do for dog aggression is because he knows your brothers dogs,have him go over there but with all dogs with muzzles on and let them play-don't have the other dogs come to your place as it will make your dog angry since he already has dog issues

as for him freezing-you really have to be careful when dogs do that,that could mean they may bite out of fear and fear biters are the worst,for that the best thing to do once you get him used to other dogs is to take him to obedience classes right away and when you call up different trainers to pick the one you like explain to them the Halloween incident and the one who's answer you like the best is the one you go with