Well, the bride is a no - brainer as a main character. She's the one getting married and has the 'big tit' characteristic which might play into the story somehow. The groom, of course, is essential too. He's about to start a new life with the bride and when time stops, his reactions (when time resumes) will matter. There could also be a best man or maid of honor. They might be the ones who first notice something strange when time starts to resume, or they could be involved in some way during the time - stop, like having a hidden relationship that gets revealed during this abnormal event.
The bride would surely be one of the main characters. Given the description 'big tit', she is a central figure as the time - stop occurs during her wedding. The groom is also an important main character as he is part of the wedding and whatever unfolds during and after the time - stop will likely involve him. Additionally, there could be a mysterious figure like a time - keeper or a magical entity that has the power to stop time and could play a significant role in the story.
In a 'big tit wedding time stop fanfiction', the main characters could be the bride, who is the focal point of the wedding and the 'big tit' aspect might be something that gives her a unique perspective during the time - stop. The groom is also key as the other half of the couple. Then, there could be an old relative, perhaps a grandmother. She could be the one who has some ancient knowledge about time - stopping events. When time stops, the bride might seek her out among the frozen guests to get some answers, and this relative could end up being a crucial character in helping the bride understand and deal with the time - stop situation at her wedding.