Help with newly adopted skittish cats?

My girlfriend and I just got 2 cats, about 2 years old, from a shelter about 2 weeks ago and they have pretty much grown up in the shelter. We started them out in a smaller room to help with the transition and then let them have the basement to explore. We got a feliway diffuser and feliway spray for the basement and their blankets and beds. They are very very skittish and will let us pet them if we entice them with a string toy first but if we move they scatter and if we talk they wont let us pet them and will either hide or stare at us from a distance. They both are dying to be petted but are still uneasy with us. I understand that it has been only 2 weeks since we got them and that this is a huge transition for them but I was wondering if there is anything else we can do to help them with this transition and be more comfortable with us?