If you can write a screenplay with vivid characters and an emotional story, you will be well on your way to winning a screenplay competition. If you are going back and forth at a healthy pace between two characters even if it is a protagonist secondary character, the audience is going to maintain a healthy relationship with the characters, and begin to develop a relationship with them in equal proportion.
If you work with one protagonist for a while, ten to fifteen minutes, and then go to another one for ten to fifteen minutes, and you turn to another one it might be difficult to catch up with the first character that you are working with. Show how they act, what they say, and what they do within the first ten to fifteen pages in the script. If you do that, the audience will be hooked.