I have access to the Bishop Family book (Bishops from 1785 to 1985) by Charles Lawrence Bishop. There is a section on the related Varn and Rentz families. Most of the research includes early families from Barnwell and Colleton Counties, S.C. Many of the names you are looking for in Colleton County are in this book. My grandmother was Mary Anne Bishop Blocker; her daughter married a Crosby and there are many connections to other of the names!
I would be happy to "look up" a particular name/names for you. Dianne Blocker Reynolds