Could it be trigger stacking? Lots of little things that add up and have caused him to tip over. The proverbial straw that broke the camel's back? Life has been pretty dramatic for him recently. It can take a few days to lose the stress hormones that are created every time there is any sort of stress, whether that's good or bad stress. The guys at Absolute Dogs have an analogy which I really like : the "stress bucket". This is a bucket with a small hole in the bottom. Every time you do anything a bit icky or a bit exciting, the bucket gets topped up. So each of his interactions with Amber, just being in a new home, meeting new people and dogs, having new food, being growled at by a strange dog, going to new places on walks, getting to go off lead.... every single one of these things, whether good or bad, will be topping up his "stress bucket". Over time, the bucket is emptied through the small hole in the bottom, but it takes time to do that and, meanwhile, any additional stress is topping it up - until the bucket overflows and you get a mess.
Sometimes a dog (or human - this is equally true of us, as my recent exploits made blatantly clear) just needs a couple of days of doing nothing exciting to let that bucket empty.
I would suggest giving him a day or so where you just do really boring things together. Try to limit his access to the other dogs so they're not playing or getting grumpy with one another. Use scatter feeding and kongs (if he is into them) to promote calmness and to exercise his brain. If you do take him out, make it the most unstimulating places, otherwise just let him mooch in the garden.
You'll get there; you're not failing him, and it's not your fault. You both need time to adjust, that's all x