3 grandchildren in custody of their step-uncle in sc he wants to transfer his custody over to me in fl how does he do this legally and quickly

First its not a good idea to piggyback your question on someone else's. This can lead to confusion. You should start a new thread. So I've moved your question to its own thread.

These are your grandkids? He has to file a petition in Family Court to change custody. You have to agree to accept custody.