Hey there
To add to the previous answer yes i think the alpha training stuff is important no matter what the aggression issue. Your dog needs to know its place in the household for his and your benefit.
The alpha issues simulate what happens in the wild and i think is really important for everyone to cover.
I think part of the aggression issue may also be based around the change in the house with the new baby and possibly some protection issues around this. He may think it is important for him to protect the baby but you need to reinforce that that is your job.
The main thing is to tell him off when he is being aggressive no matter how minor or major it seems. From a simple growl or bark through to bearing the teeth and nipping you need to always tell him off.
Use a loud GRRRR or AHHHH and i always find the squirt with the water pistol idea is a great add on.
It requires that you get hold of a dog that he has not met before ie a "strange" dog.
Get him to sit while on the lead 5 metres from the other dog. If he behaves he can advance one step forward and then is asked to sit again. Good manners means he gets to go forward, but bad behaviour needs to be reprimanded just like above and wait until he is well behaved.
On the first few sessions get the dogs within half a metre of each other but don't let them meet. After a few sessions they can meet but must both be on a leash and only gentle play is allowed. After a few times doing this let the strange dog off the lead but keep your boy on it.
Keep up with the praise and reprimanding. Eventually you will be able to let them off together but keep an eye on them.
After he has mastered this you can try the same sort of thing with dogs out on a walk. Get the dog to sit and wait as the strange dog approaches. Again praise good behaviour with petting and attention and reprimand bad behaviour as i mentioned.
If he gets to out of hand you can take him away and try again later.
Now be patient and the better he gets the more strange situations you can take him to eg dog parks.
Good luck and post if you need more help
Kate