Now Spike needs to play both the librarian and Belle's father because of 3 reasons one: he is the only character that works in a library other than Twilight,  two: he actually  takes care of Twilight. When she gets really worried and starts freaking out, it's up to him to calm her down, and three: I will explain in the next video.

P.S. I do not own my little pony or Beauty and the Beast