Stains in julep cups

We have stains in mint julep cups which have been used for various purposes over the years. some seem to be rust stains and others have a greenish cast but are not tarnish. All of these are in the bottom of the glasses and we hate to serve drinks from them. Any ideas how to clean?

From your description, these are silver plated, probably over brass base material. The silver was originally very thin on the inside, and has worn through, exposing the brass which corrodes brown/green.

You can try polishing the inside, and may get them less yukky looking, but the only real solution is to have them replated, which may cost more than buying new ones.

Silver plated items, especially ones which are functional, have to be considered disposable.