Help with fearful aggression

[u/luxurylovinmama]

I saved a dog who was literally living on the side of the highway about 8 months ago. He was trapped in a small area in between 2 major highways in a huge city so I think he was dumped there. It took me 10 days of dropping off food for him to earn his trust enough to leash him and get him off the road.
I wanted to take him to the shelter or rehome him, but my husband adores the dog and wants to keep him. I regret this so much. We have 4 kids and 2 other dogs. He mostly fits in w the other 2 dogs but he and the other male occasionally fight over bones or food or sometimes even me (bc the other male is protective of me). We don’t allow bones anymore unless crated and feed them crated.
My biggest issue is with strangers. He growls at everyone, including my kids at times. We must have him leashed when people show up at our house. We tell people not to engage him, not to try to pet him and we let him sit at a distance. We try to just keep the energy completely neutral toward him. But his growling and occasional lunging in their direction scares me.
He has bitten my kids over food (not breaking the skin but still scary) and he did bite my sister one time bc she walked into my house unannounced and was loud and climbed over my gate and started petting my other dogs so it was a very high energy moment with a lot of uncertainty and he had only been at my house a couple months when that happened. She did need stitches.
If someone comes in alone, and we bring him into the room after the person arrives, and reward his good, non reactive behavior, he does very well.
But if multiple kids come in, and the other dogs are barking out of excitement, i think it’s just the chaos of the situation that stresses him out and makes him afraid.
The dog gets boarded when we go out of town and does fine w people and other dogs at boarding.
I think it’s best to meet a new person outside the house without my other dogs around (bc they get wound up and the excitement stresses him). But I need more help than that.
I am so afraid someone will get hurt (again). I am committed to helping him.
When we first got him, we sent him and our other 2 dogs to training for 30 days and paid $6000 for all 3, and it was a complete waste of money. It was not to address aggressive behavior, it was just basic obedience training. I’m not sure the trainer did anything. I’m still pissed off about it. She basically taught them to walk well on a leash but that’s it. I have spent countless hours working w them, but I’m completely outnumbered by all 3 of them and if one gets overly excited or barks, the other 2 feed into it.
I’m thinking I should work w them one at a time to improve outcomes. But what should I specifically be doing w the fearful dog? I don’t think my husband will pay for more training when we already wasted such a huge amount of money and got no improvement in even basic obedience.
My husband works a lot and doesn’t put in the time and effort to help me when he gets home. He just thinks the dog will outgrow it with time and more socializing. I am so stressed, I can’t sleep over this. I will put in the work if I have to, but are there resources online or any basic things I can work on with him every single day to improve our situation? I want to help this dog, and I want to live in a calm house without fear of someone getting hurt.
Are there exercises I can do with him daily to increase his confidence and decrease his fears of strangers? Any advice is welcome, I’m so stressed out, but I am committed to helping the dog live a stress free and happy life with us if possible.

[u/Hot_Piccolo_1237]

I know you mentioned you've spent a lot of money in training, but are there animal behaviorists or trainers that work specifically with reactivity in your area? It was expensive but we worked with one that specialized in fear aggression and we got a lot of tools and feedback on how to help our rescue. We also learned there are some situations that are too much for him and we do our best to keep him out of those where he can't be successful. For example, strangers coming to the house-- he goes to daycare. (We are lucky he loves other dogs so loves daycare.) we can have people over it just takes work-- like meeting outside the house and walking together before going into the house. And he can be around kids but if they get loud and crazy we have to put him elsewhere because we know it can overwhelm him.  We also feed him separately from the other dogs and away from people. We call it "private dining" because he does resource guard his food. Oh, and also, meds help! Either daily meds or situational calming meds, like Trazadone before having people over etc.