Ebay is not a good place to sell fine art. There have been a few online art auction sites that have cropped up... I think Sotheby's had one. Then there's Butterfield's...
An auction will take 15% or more, and a gallery, 50%.
There's probably some place online that you can successfully advertise the Nagels. As you know, the best sale will be directly to a buyer. You can try here:
http://ewanted.com/pw/Art-15000