By letting them go before 12 weeks you are making a transition onto a new home more difficult for them. They will be tramatized, not have very good potty habits, and have a difficult time socializing.
They need as much time with mom as possible. Its like taking a 10 year old child out of the home and expecting them to live on their own because they know the basics of taking care of themselves.
I start my vaccines at 8 weeks. I do the 1st FVRCP and a dewormer. At 9 weeks I do the first FELV. Every 4 weeks they get the same vaccine again. DO NOT give more than one vaccine per visit. Many cats have died because of serious vaccine reactions b/c they had more than one shot per visit. Rabies is done at 16 weeks, but the new owners can do that.
Enjoy the babies. They get too big too fast!