Hi gibby and welcome,
I think this is fixable as well (with additional help) and a couple of things come to mind right away. Dooger wants to be king, but there can be only one.
There is a mindset that I subscribe to, that everything belongs to you. The couch, the toys, all the food - everything. Dooger should look to you before deciding what to do. Especially now.
Dooger is showing signs of dominance and aggression when on the couch -
Couch belongs to you. Get dooger off that couch. Never allow him on it.
(How to get there safely is the issue)
Instead, get a dog/bed or blankets and put that in the corner. That is his lying down space.
Toys should never be left out - they belong to you.
They should be given from time to time by you and when you are ready to take back YOUR toy, dooger needs to sit quietly and give you back your toy.
(How to get there safely is the issue)
Usually food rewards and ultimately petting or 'good dog' rewards is all that should be needed to get your dog to respect you 100% of the time.
I think you are on the right track though seeking the extra advice
If you are looking for extra high quality info (not free though) - Tenderfoot Training were experts on this site for years. They have an awesome
dog obedience training course
They show you drills and how to lead your dog with love.
For now dooger should not be left unsupervised when kids are around. not ever. Supervised, using common sense - possibly.
Being aware of the precursors to a bite (hackles up, showing, teeth, growling) is not difficult if dooger is in eyesight. It makes sense that kids should be closer to you than they are to the potential lunging distance of the dog.
Hope that may help and feel free to ask additional questions.