Not a professional and you should reach out to a dog trainer if possible.

In the meantime, negative reinforcement will not give you the desired responses. You could end up increasing reactiveness, justifying their behavior or having them only fear and listen when you're around.

Instead a lot of the basic rules of parenting a toddler applies. Positive reinforcement and distraction techniques are preferred from trainers I've worked with. Treating the chewing is easier than responding to the aggression. But training overall will help both.

If you have something they want more, they should give up what they took.

• Training them the leave it command can be helpful.
• see if you can get more toys or other things they want to chew. Chewing can be a sign of boredom.
• It may be substantially easier to train in a more neutral environment, indoors, on leash, etc (such as a room they don't normally go in)
• as others said, keep items out of reach. Only give him things they enjoy when they are in their space (such as a create or room)

This article has some information about possessive aggression that seems to provide good information.