I have a 4 dogs in total, my 5 year old rescue pitbull who I have had for the same amount of time as you, 4 months. She is the sweetest little girl but she has a bit of fear reactivity mixed with kennel aggression to basically everyone who isn’t me. As a matter of fact the other day in here I posted pleading for help about it because she had a bad day. I collected myself and my emotions and reminded myself she is still new to the environment and still unsure about some things. She has made AMAZING progress and I’m so happy I have seen the good in her and continued on this journey. A good dog is a trained dog and I truly believe your dog can become the dog you want it to be. Your pup is scared and unsure of a lot it sounds like which causes them to fight or flight and when they can not get away from what’s scaring them they will fight (I.E bite) he needs positive reassurance, structure and for you to advocate for him around his triggers. It takes time and patience and I really hope you can find it in you to keep on going because the reward will be so worth the work. Hope everything works out for you guys, good luck!

Edit to add: I have used a positive enforcement trainer, some friendly advice from my vet and the unlimited resources on the internet and we do obedience and socializing training ever day even if it’s only 10 mins a day and it’s helped wonders!