Hello - I see your post is from 2018 but wanted to comment here. First things first, if the domain(s) are undeveloped then park them with attractive landing pages. Epik offers premium parking which offers multiple templates to review and select from. You can also add additional custom content. From there I would list the domain(s) for sale as well. As for listing across other platforms, make sure you are reviewing their commission rate and the buying/selling process. If you are looking to drop any domains, first list them on https://nameliquidate.com/ and try to make something from them.
This too is a great source for knowledge: https://domaingraduate.com/en/. Chapter 9 is best for buying and selling information. Happy selling!