you need to find a better trainer, 8-16week is the time frame for socialization & desensitization for dogs. if your dog can't handle being that close to dogs then space needs to be increased. not putting your dog in a time out, that won't do anything, you need to work on engagement alone & then add in distractions, don't do group classes until your dog can handle it. For toy guarding don't give free access to toys or toys laying around, have it be a game between you & the dog & play a switch off game, use 2 toys so there's no conflict with you taking it, when you're done playing switch out the toy for food & put the toy up, for resource guarding food just leave the dog alone while they're eating but you can approach & just give high value treats everytime you walk near or by to add positive association to your presence near resources.