yes, you can tame feral cats. My wonderful cat Enza was feral. I trapped her when she was 4 months old and she came around slowly but surely. The best way to tame a feral of course is to trap them and isolate them (like in a bathroom or a large cage). But the way you are doing it will work too, especially with some cats. You do need to trap them to neuter them, or you will have 8 feral cats by spring.
THere are some videos on youtube that can help you with this as well.