I think this video is very sweet. I agree that you need to be watchful of the two, but Murphy is obviously on the ball with how tiny her little sister is. You can even see at :44 into the video that Murphy doesn't even put her head down hard, but feels Stormy under her and lifts her head immediately so as not to hurt her. And Murphy barely moves her paws during the whole video, just nudges the baby with her nose. I agree that these babies are fragile, but let's just say my Rocco has NO furbutt siblings, yet managed to climb onto the back of the couch and FALL OFF yesterday before I could get to him. Thank goodness he just bounced and was fine - now the living room is gated off. These little stinkers will make trouble even where none is to be had!! Unfortunately, accidents happen even under the most controlled circumstances; I wouldn't deprive Stormy and Murphy of playtime, as long as it's closely supervised.
Anyhow, I think that they are just precious together and Murphy is a darling girl!