Would it help to start them all as you would socialize a feral kitten, before they get hissy? Almost as a preemptive measure to pair handling and human interaction with positive things such as delicious food? Here is a link to ASPCA Pro on socializing feral kittens. Maybe it could help? https://www.aspcapro.org/resource/how-use-food-socialize-kittens
Maddie’s Pet Forum
Maddie’s Pet Forum was developed to increase collaboration in the animal welfare industry and support pet caregivers all in the name of lifesaving. Shelter and rescue organization professionals and volunteers can communicate, collaborate, ask questions, and share expertise publicly in the forum and also privately within communities and groups created in the forum.