If you truly love them and they are a rare dahlia, I would dig them up and take them. They are considered an annual where we live. If they helped you sell your house, then it is a small investment to make a good sale. The new owner may want them. Check it out with them.

If moving them, take a big chunk of soil so as not to disturb the roots, and put in a large pot. Once potted, they can readily be moved. I don't think I would try to split them at this point.

You could do as jroot suggests to move them & also cut them back to a foot or two tall so they don't have as hard a time adjusting to being dug up. You'll miss a few series of blooms but still the plant will come back from the leaf joints & bloom later in Sept & you'll have tubers for next year.