Isn't this picture cute? It's the Olsen twins with the baby twins on the show Nicky and Alex. As you can tell they are on the Full House set.
Isn't it cute?

MaryKate is on your left side, and Ashley is on your right side. I have no idea how to tell Nicky and Alex apart.

I'm not sure as of yet. Nick and Alex are babies from season 5. Can you tell the difference, Mary-Kate is holding Nick in the carriage and Ashley is holding Alex in the other.