I see. That's actually easier for you because you won't have to try to find the houses you want to see and you won't have to drive. Instead of a cooler bring a big snack bag (wrap cold drinks in face towels from your hotel), because there are plenty of places outside most of the big houses to sit and eat. Snacks on site -- if they even have them -- always cost a fortune, so this way you have options.

And be sure to check out all the proposed plantations on the tour before you go, starting with Wikipedia and working out from there. I wrote a much longer comment upthread, but the best way to know whether a given house is doing right by its own history is whether they have bothered to recreate or restore the slave quarters, and/or are supporting studies and archaeological digs at the slave quarter sites. Both Laura and Evergreen have that. But you should already have a list, so it will be easy to check out. Have a great trip!