The other two are actually part of a series someone is working on. Both are covers dedicated to specific ponies. I guess he plants to hit the other 4 eventually.
1.) "Rarity's Pipes" [Art of the Dress + Pokey Pipes Remix]
2.) Pink Pony is Best Pony (Pinkie Pie Love Song
3.) Back to the Apple Orchard (An Applejack Love Song)