You cannot have single Publish URL for multiple assets. Each Asset has associated publish URLs. Each Publish URL is also associated with specific Access Policy.
What you want to achieve is called PlayList. And, if PlayLists might be supported from products like IceCast or other, they are not supported in Azure Media Services.
You have to maintain playlists within your media application. And populate playlist items with the publish URLs of the Media Assets you want in each playlist.