
I've only used a Halti once, and found it worked well. However, I got the dog used to it by only putting it on her for meals for about 2 weeks. She learned that it meant
food!!!!! (one of her great joys in life). But as it has negative associations for your dog that probably wouldn't work.
When my two boys were pups together they had to be taken out separately, if I was the only one. If my husband was walking as well, we could have one each, so they had a bit of one-to-one. But they still relied on each other rather than us, and even had to greet each other ecstatically if they were walked one either side of a car - they couldn't bear to be parted. They could only be let off the lead together in a very secure place, because they would just run and run for the joy of it, with no thought for where they were going or where we were - it was a nightmare.
To be honest, when they were being walked together they learned very little if anything - it was only the individual walks that did any good training-wise.
Sorry.