Has anyone had success selling your parents' stuff on Ebay or Etsy?

There is no general answer to that question. It depends on the pattern and condition. Some patterns sell well. Others you can't give away. You have to look to see if there is a market for the thing that you're selling. In general, ceramics (pottery, porcelain, china) do not sell well, but there are many exceptions. The thing that make heavy things harder to sell now online are the shipping costs, which can be staggering. These that don't sell well online may do better in a yard or estate sale.

Vintage collectibles often sell well. Check out sites such as Ruby Lane or Etsy to see what they are selling and what types of prices are being asked. Small collectibles that are popular and jewelry are so much easier to ship than porcelain or glass. Many things have a good market. But to tell the truth, most things people have is usually "junk." There is so much that was made that it doesn't have any real value.

If you do a lot of research, you may find you have some treasures. I wouldn't bother to put the junk online. People won't buy it. Like I mentioned, it goes much easier in a yard sale.