Maybe you don't need to take it this far, however something like what we did with a rescued horse might work. Our farrier said he should be put down. Dad wasn't going to do that. I asked the farrier what could be done. He suggested I put a chair near the gate and leave an
apple or pear on a post several posts down. Each day move the chair a few inches closer. I did homework to have something to do while waiting. The farrier said leave the horse alone, don't look at him, don't approach him, don't make fast moves and be still as possible until he walks away. About six weeks later I was a few feet from the post with fruit on it. One day I rested my hand on the
fence post and held the fruit. The horse took it. A couple days later he came into his stall while I was mucking and putting
hay down. I ignored him, finished up a little more quickly than usual :.) and climbed the stall wall to sit and watch him so I could also get out if he got wonky. He just ate his hay. That became a habit for a week or so. One day I noticed our barn cat sitting on his rump while he was eating hay. I slid one foot onto his rump next to the cat and he was okay with it. A few days later I slid off the stall wall onto his back and he just ate his hay. Then he walked around with me sitting on him. Next day I put a hay string through his halter and let him feel it on the sides of his neck. I made sure he could see or feel where my hands were at all times and moving slowly was important. The next summer he was doing some reining and eventually going around barrels in one of the ponds :.) And sometimes I slept on the hay with him ^.^
Ptience and going slow cannot be overemphasized. He went from almost being glue and wearing apparel to forever being an amazing part of my life <3 While he was healing, it was important he be around us on his terms. When he began trusting, it was important not to undo that. He gave back all the gentle kindness he'd been shown and then some. Never had to break him. Only had to show him something new and go slow with it.
Given time, your donkeys can come around to feeling safe around you. And others, too, if they take the time needed. A soft muzzle nudging you for a cuddle or a treat feels so good it's worth the wait.
I will add that he wore the same halter Dad brought him home with, for months. It was probably 3-4 months after we had him that he would let anyone move toward his face because he'd been beaten so badly. His poor mouth had been scarred with rope and... yeah.
You can bet your donkeys are skittish for a reason, even if only because they haven't been handled or not handled properly. About leaving the halters on for now, maybe something can be done where the halters catch. Hang or lay something over that spot?