If they're old, they're worth more.
American carnival glass is really its own special area of collectible in this country, and it's something I don't know much about. I know a lot more about the reproduction piece than I do about the originals, as I handle a lot of Fenton made from the 1920s to the 1970s, after the end of the Carnival era.
I can direct you to this site:
http://ddoty.com/persmedallion.htmlThe values listed are culled from eBay, which I generally consider to be wholesale prices for all but the rarest things. If they were sold through an online shop, I'd expect the price to be higher, but I don't know by how much. If you do decided to sell them online, keep in mind that the audience of collectors for these are mostly in North America, so you'll have to take international shipping in account. Fortunately, shipping from the UK to the US or Canada isn't completely outrageous.