They are very pretty and obviously terrified at the moment. Poor babies! You sure are going to have your hands full but I have no doubt that they will be purring bundles of love in no time!
My only piece of advice to you is that if one or two seem tougher than the others than seperate them. The most dominant will lead the others and if he/she is being hard to tame the others will follow. That is always the first thing we did at the shelter and it was much easier to tame them one on one without influence from another. It's hard and sad to seperate them but if they are super feral it may be necessary.
The rest is just lots of time and patience. You are a great cat person so your instincts will tell you when to push and when to back off so as not to overdo and scare them forever. Let them learn to trust you, never stare them in the eye, and good luck! Just about the time you get them calmed down you have to haul them to the vet to get spayed/nuetered and then you have to start all over again!!

Keep us posted on these cuties!