Trying not to rag on you, but I would caution you against using terms like “nasty” to describe a living, feeling thing that just does not know better. They are not nasty. They are scared beings that feel their survivability is being threatened, and they are just trying to survive the best way they know how.
I really like the Bathroom Method for reforming feral cats. I have a 100% success rate with it, but it requires time. You lock them in a small room (such as a bathroom) with food/water/bedding. Don’t free feed them; you bring the food in and place it adjacent to you where you sit quietly. Ideally, you sit with them until they eat - which may take a while. Leave after they eat, and rinse/repeat. After a few days of this, start staying in the room with them after they finish eating. I like to read a book. Talk to them so they become acclimated to your voice, but don’t stare at them. You can move the bowl closer to you each day, with the eventual goal of them eating next to you. Plan on a half an hour each day. Once they look just watchful and not scared, try to play with them. Most ferals respond well to feathers on a string. Your goal is to get them out of whatever they are hiding behind (usually the toilet). Even a smack at a toy is a win. Do this for a month and you just may have a lap cat.
Cats - especially ferals - can be “bad patients” to handle in a stressful environment, but that doesn’t make them nasty. So much of what we ask of them in a clinical setting is incredibly unfriendly to cat species.