I have intentionally alternative the colour tone of the scenes to distinguish them and boost the impression of the themes visually. As suggested by Jessica, I will put these three clips in one, with the Comedy theme coming first, then the Realistic theme and finish with the Beatboxing theme. To make sure the audience have a balance state of listening after the previous theme, I have put white noises between every theme with black screen only showing the next theme.
It was not difficult to import all three themes into a single session simply by using the import data function (option + shift + i on mac). Once I imported everything, I first put these sounds in the correct position with the spot mode in Pro Tools. Have a look at my session:

As I was checking the session. I recognised that the comedy theme is very quiet while the Beatboxing theme is too loud. To solve the problem, I tried to route all the tracks from each theme to an aux track according to their themes for better control. Unfortunately, for some reason there is no sound nor signals coming out from the aux track. I assume this happen because there may be issues on playing a mono/stereo track to a 5.1 output (But it plays normally on a normal track that is a stereo clip with 5.1 output). That was unlucky, but still there is solution for that. The solution would be increasing the clip although I feel that this is not a good way but at least it is working.
And I guess that is the end of the project. Honestly, it is hectic, very hectic. But I have tried something that I have never done before and in the end it doesn’t look too bad as well. As an art student, the process is always the best thing of the entire production. I can definitely feel the joy and I know I am enjoying it especially when I experiment different things in a way and messing it up. After this project, I guess I am actually quiet a chaotic person.