The op is looking for advice other dog owners have gone through similar not everybody is equipped to access a behaviourist immediately and looking for tips so I think people can ask strangers on the internet
There you go. You know best 🙄
OP ignore all advice about not hand feeding. Bring in a recommended, qualified behaviourist. Joe Bloggs on the internet will not be able to give you sound advice. You need someone who you can speak to, and who can get to know your dog in order to effectively work with him.
Nobody else can advise - especially Mrs Jay who thinks what worked for her dog will work for yours. No two dogs have experienced exactly the same abuse.
Honestly, you need to bring in an expert to help your dog. Anyone can place food in a dogs bowl, close the door and let him eat. That is not the way forward for your dogs social learning.
I have rehomed many dogs - Most with resource guarding issues. I have learnt many strategies for dealing with their, unique, issues, from behaviourists. I will not advise you because what works for one will not work for another.
Your dog deserves the best result for him, and your family, without going around the mulberry bush and potentially making the problem worse. Good Luck!