What ceremony occurs before the oficial wedding

wedding custom in viet nam is quite complicated . Before an official wedding of a couple, a ceremony of engagement must be held first. In accordance with Vietnamese tradition, engagement ceremony is an official occasion for families of fiancé and fiancée to mark their relationship and to arrange the wedding. Each family need to prepare a representative who is a family member having a happy life and high-ranking position in the family. In the day of engagement, the representatives of two families will have some announcement about the wedding and exchange gifts. The time of wedding is chosen suitably based on lunar calendar. Gifts which are put in trays are prepared by the family of fiancé a few days before the engagement ceremony. The number of trays must be an odd number. In Vietnamese habits, odd numbers are thought to bring luck to the couple. In the trays, there are betel leaves, areca nut fruits, wine, tea, husband-wife and sticky rice.In the wedding day,the couple has to stay apart to avoid unlucky things.The wedding ceremony starts in front of the ancestor altar.The master of the wedding ceremony will declare the couple becomes a new family.
1. what ceremony occurs before the oficial wedding ?
2.Who is selected to be the representative of each family ? 
3. wwho prepares gift trays for rhe engagemant ceremony?
4. wwhy must the number of trays be an odd number?
5. wwhere does the wedding ceremony occur?