Hi madam, I have to say I have experience of this, I already made a similar video for a guy's birthday, mixing all cell phone videos sent by their friends, and creating a single message with all them. I understand that you want to make a video where all friends sing as one the Birthday song and maybe use splitted screen, which by the way I just delivered a music video using splitted screen. I am a professional filmmaker and video editor, I have all skills you may need and experience. So I can create a great video for you and also do some magic with after effects to improve image quality, colors and more for each video you provide me. As you can check I have 100% of customers satisfaction, so you can be sure that from me you will get a outstanding video design. If you have any question please contact me.