although Max is a bit of a thug he has the most amazing temperament and is great around other dogs x Let's just re-phrase the word thug and turn it into a zest for life.

Everything is exciting and he will go bounding into it head first, this is IMO the worst stage of a dogs life, the dreaded adolescent, where selective deafness is pretty normal. You've already been given some great advice, one to one training is a
must! You have to train and teach him seperately. I would definitely feed him seperately if he snatches, he wouldn't get it unless he sat, if he doesn't sit first time, turn you back on him for a few seconds, then turn around and ask him to sit again, then give him the food. But he has to learn that he can continue to be Mr Boisterous (age related) but with manners.

The best thing of all will happen in another few months, he'll begin to lose his puppy privileges and your other 3 dogs will begin to tell him off and put him in his place, he will learn to calm and behave less OTT around them and this will also help you to take control.
Just to reiterate, this isn't a quick fix, slowly over weeks, possibly months, often when we give advice people think it should happen immediately, it doesn't!

Especially, not when you are coming in so late as the authority figure, forgive your youngest a lot of his behaviour, he isn't really naughty, just at that age when he will challenge authority and want to do his own thing, much like some of our teenage children.
But, with your guidance he will turn into a well behaved dog like your others, mainly are. Good thing about GSD's being owner orientated, the dogs will soon look to you first and be loyal companions, but do bring your teenagers in to also help. I trained my brothers GSD's even now years later they are as close to me as my brother who they live with and who is their owner, they never forget who trained them and gives them the love, affection and attention, and they can have more than one authority figure, sometimes I don't see them for months, but they will still come to me often even before my brother.

If your teenagers are involved too, it will bond you all to the dogs.
You may even find some of the dogs work better with other members of the household.
Good luck, your doing brilliant.